JP5379725B2 - Alarm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alarm which is easily installed and formed thin. <P>SOLUTION: The alarm is provided with: a case 1 which stores a sensor for sensing the change of a peripheral environment; and a mounting base 4 whose outer shape from a front view is a circular shape and which can be fixed to an installation surface where the case 1 is relatively rotated along the circular face of the circular shape relative to the mounting base 4, and a case side engagement section formed in the case 1 is engaged with a base side engagement section formed in the mounting base 4 in the circumferential direction of the circular shape, and thereby the case 1 can be mounted to the mounting base 4. The alarm is formed so that the mounting base 4 is provided with one or more protruding parts 41 protruding in the direction of the outside of the diameter of the circular face at the outer peripheral section, and when the case 1 is mounted to the mounting base 4 in the front view, the protruding part 41 is made to be visible, and when the case side engagement section is engaged with the base side engagement section, the protruding part 41 is concealed behind the case 1. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an alarm device installed on a wall surface or a ceiling surface.

  Conventionally, as an alarm device installed on a wall surface, a ceiling surface or the like, as described in Patent Document 1, for example, a front view circle that houses a sensor unit (in the literature, “detection unit”) that senses changes in the surrounding environment A case portion (“main body portion” in the literature) and a circular mounting base portion (“base portion” in the literature) having the same diameter as the main body portion, and the base portion is first fixed to the installation surface Later, there was one that attached the main body to the base.

  In Patent Document 1, as a configuration for attaching the main body part to the base part, a case side engaging part ("protruding member" in the literature) formed on the main body part by rotating the main body part relative to the base part; The base body part is attached to the base part by engaging the base side engaging part (in the literature, “annular groove”) formed in the base part in the circular radial direction. In order to align the main body and the base, the bottom of the main body is flared in the radial direction to form a guided part ("insertion protrusion" in the literature), which is inserted into the surface of the base. An annular guide portion (“side wall” in the literature) corresponding to the shape of the protrusion is formed. The protruding member is formed to protrude in the radial direction on the outer peripheral surface of the inserting protruding portion. An annular groove is formed on the inner peripheral surface of the side wall. And the guide groove which guides a raising member to an annular groove is formed in the internal peripheral surface of a side wall.

  According to this configuration, since the main body portion and the base portion have the same shape, the mutual shape serves as an index, and it is easy to fit the insertion protrusion into the annular side wall. Thereafter, while the main body portion is rotated with respect to the base portion, the protruding member is guided by the guide groove and is fitted into the annular groove.

  Further, Patent Document 1 has a configuration in which a guide groove is not provided, a claw portion of an elastic body is provided instead of a projection member, and the claw portion is fitted into the annular groove by pushing the insertion projection portion into the side wall. It is disclosed. As a similar configuration, Patent Document 1 also discloses that an engaging protrusion is provided instead of a protruding member without providing a guide groove. The engaging protrusion is always urged radially outward and can be optionally retracted radially inward. With the engaging protrusion retracted radially inward, the insertion protrusion is inserted into the side wall, and the engaging protrusion protrudes radially outward again, so that the engaging protrusion is engaged with the annular groove. Match.

JP 2010-33286 A

  By the way, the case portion is not limited to the same circular shape as the mounting base portion. The case portion may have a shape different from the circular shape of the mounting base portion in front view, for example, a square shape. In such a case, from the viewpoint of design, it is customary to make the shape of the case portion in front view larger than the attachment base portion so that the attachment base portion is hidden behind the case portion in front view in the installed state.

  However, in the alarm device described in Patent Document 1, when the main body and the base are different in shape, when the main body is attached to the base, the entire base is covered by the main body. Accordingly, it is difficult to grasp the position of the side wall of the base part, and there is no center alignment index, and it is difficult to fit the insertion protrusion into the side wall. As a result, it may take time to align the main body portion and the base portion, and there is a possibility that quick installation work cannot be performed.

  If the thickness of the mounting base portion is increased, the distance between the case and the installation surface increases, and the case can be viewed from the side, making it easy to align the center. However, this increases the thickness of the entire alarm device. Furthermore, when the alarm device is disposed in the living space, if a mark for centering or the like is provided, it may not be suitable for the design of the living space.

  In view of the above circumstances, an object of the present invention is to provide an alarm device that is easy to install and thin even if the case portion has a different shape with respect to the mounting base portion.

  A first characteristic configuration of the alarm device according to the present invention includes a case portion that houses a sensor portion that senses changes in the surrounding environment, and an attachment base portion that has a circular outer shape in front view and can be fixed to an installation surface. A case-side engagement portion formed on the case portion in the circular circumferential direction and the mounting base portion by rotating the case portion relative to the mounting base portion along the circular circular surface. One or more protrusions that can be attached to the mounting base portion by engaging with the base side engaging portion formed on the mounting surface, and the mounting base portion protrudes radially outward of the circular surface. When the case portion is attached to the mounting base portion in a front view, the protrusion is visible, and the case side engaging portion and the base side engaging portion are engaged. When the projections are Lies in the arrangement so that hidden behind the case part.

  With this configuration, when the case portion is attached to the mounting base portion, even if the mounting base portion is covered with the case portion, one or more protruding portions can be visually recognized. Easy alignment with the mounting base. When the case side engaging portion and the base side engaging portion are engaged, the projecting portion is hidden behind the case portion, so that the design is not impaired.

  According to a second characteristic configuration of the alarm device according to the present invention, a guide portion that guides the case side engaging portion to the base side engaging portion is formed in the mounting base portion, and the guide portion includes the guide portion. The guide portion is formed in such a manner that the relative rotation of the case portion is allowed by being fitted into the case, but the relative movement of the case portion with respect to the mounting base is prevented.

  With this configuration, the guided portion and the guide portion can be opposed to each other, and the relative rotation center thereof coincides with the relative rotation center of the case portion. Therefore, when the guided portion is fitted into the guide portion, the alignment between the case portion and the mounting base portion is achieved. Furthermore, the guided portion and the guide portion guide the engagement between the case side engaging portion and the base side engaging portion. As a result, it is easier to align the case portion and the mounting base portion with the protrusion as an index, and the operation of attaching the case portion to the mounting base portion is facilitated.

  A third characteristic configuration of the alarm device according to the present invention is that the guided portion is configured to be fitted into the guide portion in stages by relative rotation of the case portion.

  According to this configuration, the guided portion is fitted into the guide portion step by step. That is, due to the relative rotation of the case portion when the case portion is attached to the attachment base portion, the separation distance between the case portion and the attachment base portion is narrowed. Further, when the protruding portion is hidden behind the case portion, the protruding portion and the outer peripheral portion of the back surface of the case portion do not interfere with each other. Therefore, when the case portion is attached to the attachment base portion, the attachment base portion can be retracted to the case portion in a side view. As a result, it is possible to provide a compact alarm device that can be reduced in thickness only by rotating.

  The 4th characteristic structure of the alarm device which concerns on this invention exists in the point which provided the fixing | fixed part which fixes the said mounting base part to an installation surface in the said projection part.

  With this configuration, since the protrusion as a member for fixing the attachment base portion to the installation surface can be used as an index for centering, an increase in the number of components can be prevented.

(A) is a perspective view from the front direction of a smoke detector. (B) is a perspective view from the back direction of a smoke sensor. FIG. 3 is an exploded perspective view from the back side of the smoke detector. These are perspective views which show the relationship between the base fixed to the wall surface, and a case. FIG. 5 is a rear view when the case is attached to the base. These are figures which show the point when attaching a case to a base. These are figures which show the state of each part when a guide part is located in the 1st step part. These are figures which show the state of each part immediately after a guide part fits in the 2nd step part. These are figures which show the state of each part when engagement hooks engage. These are figures which show the state of each part when a protruding part has overlapped.

  Hereinafter, an embodiment in which the present invention is applied to a photoelectric smoke detector will be described with reference to the drawings. In FIG. 5, (a) is a front view when the case and the base are aligned, and (b) is a partial sectional view in front view showing the relationship between the guided portion and the guiding portion at that time. (C) is a longitudinal sectional view in FIG. 6 to 9, (a) is a rear view of the case and the base in each state, (b) is a partial cross-sectional view of the region (b) in FIG. (B) is a longitudinal cross-sectional view in the figure, (d) is a longitudinal cross-sectional view in the circumferential direction as viewed from the radially outward direction of the region (d) in (a) figure, and (e) is ( e) It is the longitudinal cross-sectional view of the circumferential direction which looked at the radial direction of the area | region. In FIG. 4, in order to facilitate understanding of the features of the present invention, the unevenness or the like expressed in other drawings is not expressed within a range that does not affect the configuration of the smoke detector. 5 to 9 are simplified for the same reason. The single-line arrows in the circumferential direction in FIGS. 5 to 9 represent the mounting rotation direction of the case, and are hereinafter simply referred to as “mounting rotation direction”. However, the mounting rotation direction is a relative rotation direction as viewed from the stand of the case, and is reversed when viewed from the stand of the base.

  In the following description, the surface opposite to the wall surface is defined as the front side (front side), and the surface on the wall surface side is defined as the back side (rear side).

[About overall configuration]
As shown in FIG. 1, the smoke detector allows inflow of smoke from the side peripheral surface, and has a square case portion (hereinafter referred to as “case 1”), a substrate 2, and a case portion in front view. And a photoelectric sensor part (hereinafter referred to as “sensor 3”) that can sense smoke flowing into the case part, and has a circular shape smaller than the square shape of the case part when viewed from the front, An attachment base portion (hereinafter referred to as “base 4”) that is fixed and to which the case portion can be attached is provided.

  The sensor 3 detects the smoke flowing into the case 1 and emits an alarm sound from the speaker 5 when the smoke concentration exceeds a preset threshold value. To stop the alarm sound, the alarm sound can be stopped by pressing an alarm stop button 6 disposed on the surface of the case 1. If the alarm is installed at a high place and the alarm stop button 6 is not reachable, the alarm sound is stopped even if the alarm stop string 7 that can be hung down from the case 1 is pulled.

  As shown in FIG. 2, the case 1 includes a base portion (hereinafter referred to as “rear case 1a”) on the rear side, a cover portion (hereinafter referred to as “front case 1c”) on the front side, a rear case 1a and a front portion. And a partition portion (hereinafter referred to as “intermediate case 1b”) that partitions the internal space of the case 1 surrounded by the case 1c in the front-rear direction. The front case 1c, the rear case 1a, and the intermediate case 1b are made of resin and are manufactured by injection molding. The case 1 houses a sensor 3, a substrate 2, a speaker 5, an alarm stop button 6, and the like.

  Although not shown, the sensor 3 includes a plurality of smoke inlets through which smoke can be introduced, a plurality of labyrinth-like wall portions juxtaposed via a gap so as to block light from the outside, and the interior of the sensor 3. And a light receiving unit for sensing light from the light emitting unit scattered by the smoke flowing into the sensor 3. Since this sensor 3 is already known, the mechanism of smoke detection will not be described here.

  As shown in FIG. 2, the sensor 3 is disposed on the substrate 2 and a speaker 5 is connected thereto. The board 2 is printed with an electric circuit (not shown) and provided with electronic parts (not shown), and controls smoke detection, alarm sound generation, and the like.

  The assembly of the case 1 will be briefly described. As shown in FIG. 2, the alarm stop button 6 is dropped into the front case 1 c from the back side, and then the substrate 2 is fitted into the front case 1 c together with the speaker 5 at a predetermined position. Subsequently, the intermediate case 1 b is fitted into the front case 1 c so as to cover the substrate 2. Protrusions (not shown in the figure) projecting inward are formed on the inner side surfaces of two arbitrary corners on the inside surface of the front case 1c. On the outer surface of the intermediate case 1b, protrusions (not shown) protruding outward are formed corresponding to the protrusions of the case 1c. When the intermediate case 1b is forcibly pushed in until the leading end surface of the rising portion of the intermediate case 1b contacts the back surface of the front case 1c, both protrusions get over each other and engage. Thereby, the intermediate case 1b is fixed to the front case 1c, and is integrated with the front case 1c. The intermediate case 1 b is formed with an opening having substantially the same diameter as the sensor 3, and the intermediate case 1 b does not interfere with the sensor 3.

  Next, the rear case 1a is fitted into the front case 1c so as to cover the intermediate case 1b and the sensor 3. Finally, screws are tightened from the rear side of the rear case 1a to fix the rear case 1a to the front case 1c. As described above, as shown in FIG. 1, the case 1 that is square in front view and square in side view is assembled.

[About the base]
As shown in FIG. 3, the base 4 is fixed to the wall surface prior to the case 1. The base 4 is made of resin and is manufactured by injection molding. As shown in FIG. 4, the base 4 has a circular shape. As shown in FIG. 3, a rising portion 12 is formed on the outer peripheral portion of the rear case 1 a, and the base 4 has a size inscribed in the inner surface of the rising portion 12. That is, the shape of the base 4 is a circular shape inscribed in the square shape of the case 1. Thus, it can be said that the case 1 is made compact by minimizing the case 1 relative to the base 4, and the case 1 is stabilized by maximizing the base 4 relative to the case 1. It can be said that this is a configuration that can be supported. Protrusions 41 projecting in the radially outward direction of the base 4 are formed at four locations on the outer periphery of the base 4. As shown in FIG. 3, the protrusion 41 is formed with a hole (a “fixing portion” according to the present invention) into which a fixing tool, for example, a gypsum board pin P can be inserted, via the four protrusions 41. The base 4 can be attached to the wall surface of the plaster board. The base 4 is also formed with a screw hole 44, which can be attached with a screw or the like.

[Attaching the case to the base]
A procedure for attaching the case 1 to the base 4 will be described. First, as shown in FIGS. 4 and 5, the case 1 is inserted into the guide portion 42 while the case 1 is rotated to the left and right with respect to the base 4 fixed to the wall surface W in advance. And the base 4 are aligned.

  As shown in FIG. 3, the guided portion 16 is integrally formed at the center of the rear case 1a so as to protrude rearward. The guide part 42 is integrally formed in the center part of the base 4 so as to be recessed on the back side. The guide part 42 is formed in a shape that follows the shape of the guided part 16, and the guided part 16 can be fitted therein. When the guided portion 16 is fitted into the guiding portion 42, the cores of the case 1 and the base 4 are aligned. When the case 1 is further rotated according to the guidance of the guide portion 42, the engagement hooks 18 provided on the rear outer peripheral portion of the rear case 1a are engaged with the engagement hooks provided on the front outer peripheral portion of the base 4 as shown in FIG. The case 1 can be attached to the base 4 by being engaged with 43 in the rotational direction.

  This point will be described in detail. As shown in FIGS. 3 and 4, the guided portion 16 has an annular shape when viewed from the front, and is formed with ribs 16 a projecting radially outward at two locations on the outer peripheral portion. The guide part 42 is a hole having a shape corresponding to the annular shape of the guided part 16 and penetrates from the front side to the back side of the base 4. Two first step portions 42 a and two second step portions 42 b are provided on the outer periphery of the guide portion 42. The second step portion 42b penetrates from the front side to the back side of the base 4, but the first step portion 42a is shallower than the second step portion 42b and does not penetrate. The outer diameters of the first step portion 42a and the second step portion 42b are matched with the outer diameter of the guided portion 16 including the rib 16a. The first step portion 42a and the second step portion 42b have a certain width in the circumferential direction and are continuous with each other. In the present embodiment, both the first step portion 42a and the second step portion 42b have a central angle of 60 °. That is, when the guided portion 16 is fitted into the first step portion 42a or the second step portion 42b, relative rotation in the circumferential direction of the guided portion 16 is allowed, but relative movement in the radial direction is prevented.

  That is, the relative rotation center of the case 1 and the base 4 and the relative rotation center of the guided portion 16 and the guide portion 42 coincide with each other. Although rotation is allowed, relative movement of the case 1 with respect to the base 4 is prevented.

  Further, since the first step portion 42a and the second step portion 42b have different depths, the guided portion 16 is changed from the first step portion 42a to the second step as shown in FIGS. When fitted into the portion 42b, as shown in FIG. 7C and FIG. 8C, the distance between the case 1 and the base 4 in the front-rear direction is reduced.

  As described above, the base 4 is provided with the four protrusions 41, and three of the protrusions 41 are in front due to the rotation of the case 1 with respect to the base 4 as shown in FIG. Projects from behind the case 1 or hides in view. Specifically, since the circular shape of the base 4 is inscribed in the square shape of the case 1, as shown in FIG. 6A, when the protruding portion 41 is positioned in the vicinity of the inscribed portion, the protruding portion 41 is in the case 1. It protrudes from behind and becomes visible. As shown in FIGS. 7A, 8A, and 9A, when the protrusion 41 is located in a space between a square shape and a circular shape, the protrusion 41 is hidden behind the case 1. . The position and range of the second step portion 42 b are set so as to correspond to the timing at which the protrusion 41 is hidden behind the case 1. As for the position and range of the first step portion 42a, when the guided portion 16 is located at a location near the second step portion 42b in the first step portion 42a, the protrusion 41 is hidden behind the case 1. It is set as follows.

  In addition, by rotating the case 1 with respect to the base 4, the guided portion 16 is fitted into the second step portion 42b from the first step portion 42a, and as shown in FIGS. 7 (a) to 8 (a). When 1 is rotated, as shown in FIGS. 7E to 8E, the engagement hook 18 and the engagement hook 43 are engaged.

  With the above configuration, when the case 1 is attached to the base 4, the circular portion of the base 4 is hidden behind the case 1, but the protrusion 41 is visible. That is, the center of the base 4 can be determined using the protrusion 41 as an index. Further, since the guided portion 16 is fitted into the guide portion 42, the case 1 and the base 4 can be easily aligned. Furthermore, since the range of the first step portion 42a and the second step portion 42b is set in a wide range corresponding to a central angle of 240 °, the alignment between the case 1 and the base 4 is easier. Since the protrusion 41 is hidden behind the case 1 after the engagement hooks 18 and 43 are engaged, the appearance after the smoke detector is installed is good.

  As described above, before the guided portion 16 is fitted into the second step portion 42b, that is, between the state of FIG. 6 and the state of FIG. To do. That is, in the state of FIG. 6, as shown in FIG. 6D, the rising portion 12 and the protruding portion 41 interfere, but in the state of FIG. 7, the rising portion 12 and the protruding portion 41 do not interfere. Therefore, when the guided portion 16 is fitted into the second step portion, the base 4 relatively sinks inside the case 1. Therefore, the thickness of the alarm device can be reduced when the wall surface is attached.

  Here, the engagement between the engagement hook 18 and the engagement hook 43 will be described in detail. As shown in FIGS. 3 and 4, guide rails 45 are formed at three locations on the outer peripheral portion of the front side of the base 4. The guide rail 45 is formed in a bag shape by raising the outer peripheral portion of the base 4 in the front direction and further bending it in the radially inward direction. The guide rail 45 has a radially inner surface and at least a surface on the upper side in the mounting rotation direction open. The engagement hook 43 is formed on the back side of the guide rail 45 and on the upper side of the mounting rotation direction.

  Further, on the back side of the rear case 1a, guide rails 19 are formed at three portions that can face the guide rail 45. The guide rail 19 rises from the rear case 1a in the back direction, and is further bent in the radially outward direction to form a bag shape. The guide rail 19 has a radially outer surface and at least a surface on the upper side in the mounting rotation direction open. The engagement hook 18 is formed on the front side of the guide rail 19 and on the upper side of the mounting rotation direction.

  The positions of the guide rail 19 and the guide rail 45 are set so that the engagement hook 18 and the engagement hook 43 are engaged after the guided portion 16 is fitted from the first step portion 42a to the second step portion 42b. is there. The lengths of the guide rail 19 and the guide rail 45 are set so that the guided portion 16 can be relatively rotated until it comes into contact with the end portion of the second step portion 42b opposite to the first step portion 42a.

  Further, as shown in FIGS. 3 and 7E, the base 4 is integrally formed with a leaf spring portion 46 that is inclined to the front side. The leaf spring portion 46 is disposed on the upper side of the mounting rotation direction with respect to the engagement hook 43. Accordingly, as shown in FIGS. 7A and 7E, the leaf spring portion 46 comes into contact with the back side of the guide rail 19 before the engagement hook 18 and the engagement hook 43 are engaged with each other. 1 is biased to the front side. The distal end portions of the engagement hook 18 and the engagement hook 43 are inclined, and when the case 1 is rotated in the mounting direction and the inclined portions start to overlap each other, along the inclined portion of the engagement hook 43 on the fixed side. The inclined portion of the engagement hook 18 is guided, and the case 1 approaches the wall surface side against the urging force of the leaf spring portion 46. When the engagement hook 18 and the engagement hook 43 get over each other, the case 1 is separated from the base 4 by the urging force of the leaf spring portion 46. Thereby, the engagement hook 18 and the engagement hook 43 are engaged. Since this engagement is in the circumferential direction, once the case is engaged, unless the case 1 is rotated in the removal direction while pushing the case 1 against the base 4 against the urging force of the leaf spring 46, the case 1 does not come off the base 4.

  After the engagement hooks 18 and 43 are engaged, the engagement hook 18 can smoothly slide along the front surface of the guide rail 45 as shown in FIGS. 8 (e) to 9 (e). The engaging hook 43 can smoothly slide along the back surface of the guide rail 19. In other words, the guide rails 19 and 45 guide the movement of the engagement hooks 18 and 43 in the circumferential direction, but prevent the case 1 from moving in the direction away from the base 4. Note that the separation between the case 1 and the base 4 due to the urging force in the front-rear direction of the leaf spring portion 46 is limited to the position where the engagement hooks 18 and 43 contact the guide rails 45 and 19.

  In this way, the smoke detector is installed on the wall surface. In addition, since case 1 is square shape by front view, the outer periphery four sides of case 1 become parallel or perpendicular | vertical with respect to the ceiling surface and floor surface of installation space. Therefore, it is easy to become familiar with the installation space as compared with the case of the circular shape.

[Changing the angle of the case after mounting to the base]
Since the case 1 according to the present invention has a quadrangular shape when viewed from the front, the inclination of the case 1 is particularly conspicuous when it is installed on a wall surface, as compared with a circular shape. Therefore, the smoke detector according to the present invention is configured so that the angle of the case 1 can be adjusted even after the case 1 is attached to the base 4. This angle adjustment will be described.

  As shown in FIGS. 3 and 4, a ridge 20 having a constant width in the circumferential direction is formed on the rear surface of the rear case 1 a on the relative rotation locus of the protrusion 41 after the engagement of the engagement hooks 18 and 43. An inclined portion 20 a is formed on the upper side of the protruding portion 20 in the mounting direction of the case 1. Further, the front side of the protrusion 41 is raised to form a raised portion 41a. The sum of the heights of the raised portion 20 and the raised portion 41a is set to be larger than the limit value of the separation distance between the case 1 and the base 4 due to the urging force of the leaf spring portion 46 described above. The circumferential length of the raised portion 20 is set to be the same as or larger than the range in which the case 1 can rotate after the engagement hooks 18 and 43 are engaged.

  In such a configuration, after the engagement hooks 18 and 43 are engaged, as shown in FIGS. 8 to 9, the case 1 is further rotated to ride the raised portion 20 on the raised portion 41 a (overlapping in plan view). ), The case 1 tends to be further separated from the base 4 against the restraint in the separation direction between the case 1 and the base 4 caused by the contact of the engagement hooks 18 and 43 and the guide rails 45 and 19. However, the case 1 and the base 4 cannot basically be separated because the relative movement in the front-rear direction is restricted. Therefore, elastic deformation occurs in at least one of the case 1 and the base 4 made of resin, and resistance to rotation of the case 1 is given by the restoring force. Therefore, the case 1 is positioned on the base 4 at any position while the raised portion 41 a is riding on the raised portion 20. In other words, after the case 1 is attached to the base 4, the posture of the case 1 can be freely adjusted while being fixed to the base 1. In addition, since the inclined part 20a is provided, the rising part 20 from the state of FIG.

  From the above, the guide rail 19 corresponds to the “case side guide portion” according to the present invention, the guide rail 45 corresponds to the “base side guide portion”, the leaf spring portion 46 corresponds to the “biasing portion”, and the bulge The portion 20 corresponds to a “first resistance portion”, and the raised portion 41a corresponds to a “second resistance portion”. Further, the engaging hook 18 and the guide rail 45, the engaging hook 43 and the guide rail 19, and the raised portion 20 and the raised portion 41a together constitute the “resistance generating portion” according to the present invention. .

[Another embodiment]
(1) In the above-described embodiment, the guided portion 16 has a convex shape and the guide portion 42 has a concave shape to form the first step portion 42a and the second step portion 42b. However, the present invention is not limited to this. . For example, the guided portion 16 may be formed in a concave shape to form a first step portion and a second step portion, and the guide portion 42 may be formed in a convex shape.
(2) In the above-described embodiment, the raised portion 20 as the first resistance portion is formed in the rear case 1a, and the raised portion 41a as the second resistance portion is formed in the protrusion 41. However, the present invention is not limited to this. Absent. For example, the protruding portion 41 may be widened in the circumferential direction to form a raised portion as the first resistance portion, and the raised portion as the first resistance portion may be formed in the rear case 1a.
(3) In the above-described embodiment, the three protrusions 41 serving as the index for alignment are provided, but it is sufficient that the number of the protrusions as the index is one or more. However, if there are two or more projections serving as indexes and they are spaced apart by 90 ° or more at the central angle, the position of the guide portion 42 that is the central portion of the base 4 is easy to predict and is suitable.
(4) In the above-described embodiment, the case 1 has a square shape inscribed by the circular shape of the base 4, but is not limited thereto. If the protrusion 41 is visible when the case 1 is attached to the base 4 and the protrusion 41 is hidden behind the case 1 before the engagement hooks 18 and 43 are engaged, for example, the front surface It may be a viewing rectangle, other polygonal shapes, a circular shape, an elliptical shape, or the like. In the above-described embodiment, the square shape of the case 1 is chamfered at the four corners in an R shape, but it may not be chamfered.
(5) In the above-described embodiment, the first step portion and the second step portion are provided, and the guided portion is fitted in the guide portion in two steps. However, the present invention is not limited to this. For example, it is good also as a structure which a to-be-guided part fits into a guide part in three steps or more or a continuous side.
(6) Although the above-mentioned embodiment showed the example which installs an alarm device in a wall surface especially, the alarm device installed in a ceiling surface may be sufficient.

  The present invention is not limited to smoke detectors, but can be applied to other alarm devices that detect changes in the surrounding environment, such as heat detectors and gas alarm devices.

1 Case (case part)
3 Sensor (Sensor part)
4 Base (mounting base)
16 Guided portion 18 Engagement hook (case side engagement portion)
41 Projection part 42 Guide part 43 Engagement hook (base side engagement part)
W Wall surface (installation surface)

Claims (4)

A case part that houses a sensor part that senses changes in the surrounding environment, and an attachment base part that has a circular outer shape in front view and can be fixed to an installation surface;
By forming the case part relative to the attachment base part along the circular circular surface, the case side engagement part formed in the case part in the circular circumferential direction and the attachment base part are formed. The case side can be attached to the mounting base part by engaging with the base side engaging part,
The mounting base portion is provided with one or more projecting portions projecting in the radially outward direction of the circular surface on the outer peripheral portion,
When the case portion is attached to the attachment base portion in a front view, the protrusion portion is visible, and when the case side engagement portion and the base side engagement portion are engaged, the protrusion portion Is configured to be hidden behind the case portion. In the mounting base portion, a guide portion that guides the case side engaging portion to the base side engaging portion is formed,
The guided part is formed in the case part so as to allow the relative rotation of the case part but prevent the relative movement of the case part with respect to the mounting base by being fitted into the guide part. The alarm device described.   The alarm device according to claim 2, wherein the guided portion is configured to be fitted into the guide portion in stages by relative rotation of the case portion.   The alarm device according to any one of claims 1 to 3, wherein a fixing portion that fixes the mounting base portion to an installation surface is provided on the protrusion.

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