US2506983A - Signal control structure - Google Patents

Signal control structure Download PDF

Info

Publication number
US2506983A
US2506983A US751316A US75131647A US2506983A US 2506983 A US2506983 A US 2506983A US 751316 A US751316 A US 751316A US 75131647 A US75131647 A US 75131647A US 2506983 A US2506983 A US 2506983A
Authority
US
United States
Prior art keywords
pin
plunger
seal
spring
signal control
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US751316A
Inventor
Frank C Williams
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to US751316A priority Critical patent/US2506983A/en
Application granted granted Critical
Publication of US2506983A publication Critical patent/US2506983A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00Fire alarms; Alarms responsive to explosion
    • G08B17/04Hydraulic or pneumatic actuation of the alarm, e.g. by change of fluid pressure
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S116/00Signals and indicators
    • Y10S116/44Portable personal alarms

Definitions

  • This invention relates to a control structure that is especially adapted for giving a signal, such as for example, a fire alarm.
  • Another object of my invention is to provide a signal control structure which is relatively cheap to manufacture, and adapted for several uses.
  • Figure 1 is a part elevational and part sectional view through the structure when used to blow a whistle.
  • Figure 2 is a view somewhat like Figure l, but showing the structure arranged to give either or both visual or audible signals at a distance from the device.
  • Figure 3 is an enlarged view of the lower end of Figure 1.
  • I is a container preferably made of strong material such as steel, whereby it will withstand the pressure of 500 lbs. per square inch at 70 F., or 6000 lbs. per square inch at 190 F.
  • the container I is adapted to receive a gas or liquid such as carbon dioxide, which I have found to be satisfactory for uses to be described.
  • One end of the container I has a reduced threaded end 2 and on this is mounted a cup shaped cap 3, having a sleeve portion 4 threaded to engage the threads on the neck 2 of the container I.
  • the cup 5 is formed by the shell 5 and has its bottom I positioned adjacent a seal 8 which is welded to the end of the neck 2.
  • the Seal 8 has a puncturable portion 9 that is adapted to be struck by the piercing point IQ of a hollow pin II.
  • the piercing pin II is fastened as by welding to a plunger I 2, one end of which extends into the cup 5 and has a retaining ring I3 fastened thereto.
  • a disc I 5 that is positioned in spaced relation to another disc I6 that is fastened to the rim of the shell 6. Between the discs I5 and I6 is located material I I that is adapted to fuse at a predetermined point.
  • a gasket I8 Positioned on the disc I B is a gasket I8 preferably of non-metallic material and on this gasket I8 rests a ring I9 which supports a spring which in the form shown is made up of a plurality ,of spring washers 23.
  • the upper one of which is in engagement with the retaining ring I3 so that when the parts are shown in the position in Fig-- ure 1, the spring or its members 2E! are under considerable tension whereby when the material I? is fused at a predetermined temperature, the disc I5 is released and the spring will drive the plunger I2 with the piercing pin II upwardly so that the cutting edge of the pin will strike the.
  • a gasket 22 is utilized between the bottom of the cup I and the seal so as to insure that the gas or liquid of the container I will pass into the hollow pin I I.
  • the gasket 22 has a hole therein somewhat smaller in diameter than the outer diameter of the pin I I so as to further insure passage of the gas or liquid into the hollow pin.
  • the plunger I2 carries a cylinder 23 in which a piston 24 is located.
  • the piston has a rod 25 connected to a lever 2t through a motion pick-up means 2?.
  • the lever 25 is pivoted at 28 and its end 29 is adapted to engage a contact 30, connected to a relay R supplied with current from battery B.
  • a lamp L and a horn H are adapted to be operated through the relay contact 3
  • the structure may be used to inflate a membrane or fabric shell which may serve as a signal in some cases.
  • the gas and liquid coming from the container I may be utilized to remove heat from or freeze some material, by voluntarily fusing the metal l1.
  • a hook 32 which may be utilized for hanging the device on a suitable support.
  • the hook 32 may be of the open type or in the form of an eye.
  • a signal control structure comprising a single element container closed at one end by a puncturable seal and containing gas-or liquid under pressure, a cup shaped cap having a sleeve portion with means for attaching it over the end of the container having the seal, a plunger having at least one end extending into the cup part of the cap, retaining rings fastened to the plunger in spaced relation, a support plate fastened to the rim of said cup part, a disc fastened to the plunger adjacent the outer of said retaining rings and spaced a short distance from said support plate, fusible metal normally anchored to both the support plate and said disc, a hollow piercing pin carried by the plunger and extending into a guide hole in the bottom of the cup to a point adjacent said seal and spring means located within the cup and acting on the inner of said retaining rings to force the plunger and pin rapidly toward the seal and cause the pin to puncture the seal when the fusible metal is fused.
  • a signal control structure as defined in claim 1 further characterized in that said piercing pin spring and plunger are so co-related that the pin will puncture the seal before the end of the plunger will hit thebottom of the cup while the spring will have suflicient tension to hold the plunger against the bottom of the cup after said seal has been broken.
  • a signal control structure as defined in claim 1 further characterized in that a ring for supporting the spring is positioned on the inner wall-f the cup adjacent said support plate but preferably separated therefrom by .a heat :resisting gasket.
  • a signal control structure as defined in claim 1 further characterized in that a suitable non-metallic gasket is positioned within the sleeve against the opposite side of the cup bottom, the gasket having a hole therein slightly smaller than the outside diameter of the pierclng pin for the purpose described.
  • a signal control structure comprising a. single element container having an integral much reduced end, closed at said :end by a nonshatterable but puncturable seal and contain-- ing gas or liquid under pressure, means attachable to the reduced end of the container having the seal and carrying a device for'puncturing the seal and directing the flow of the gas or liquid Git therefrom, fusible means for normally holding tially within the hollow plunger, a spring directly connected to the plunger for driving the .plunger and pin into puncturing position to release said gas or liquid through said hollow pin andcmeansjincluding a readily meltable element for holding the plunger pin and spring under restraint 'until a predetermined temperature is reached.
  • a signal control structure comprising a single element container closed at one end by a seal that will withstand a high pressure but having a predetermined puncturable portion and containing gas .or liquid under pressure, means including a readily meltable element for holding a puncturing pin which is hollow uniformly throughout its length adjacent said seal until a predetermined temperature is reached and then releasing it and spring means alone acting solely and directly on the plunger for moving said pin when releasedbysaid meltable element and causing it to strikethe seal so as to surely puncture it and direct the quantity and the flow of the contents of the container from the pumture end of the pin through its entire length thereof and out at its oppositeend for the purpose described.
  • a signal control "structure as defined in claim 5 further characterized in that said at-'- tachable means is a cup shaped member awhile said pin moving means is a plurality of individual spring washers radially spaceda considerable distance from the pin to also act as radiating surfaces for the purpose described.

Landscapes

  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • General Physics & Mathematics (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)

Description

May 9, 31950 F. c. WILLIAMS SIGNAL CONTROL STRUCTURE Filed May 29, 1947 FIG./
- INVENTOR. F RHNK C. WILLIAMS Patented May 9, 1956 UNITED STATES PATENT OFFICE 9 Claims.
This invention relates to a control structure that is especially adapted for giving a signal, such as for example, a fire alarm.
There are many places where the ordinary fire alarm would be objectionable, both as to its looks and space taken up by it.
It is therefore, one of the objects of my invention to provide a signal control structure which is not only ornamental in character so that it may be used in any room in a residence, but one that is highly efficient and useful wherever it may be placed.
Another object of my invention is to provide a signal control structure which is relatively cheap to manufacture, and adapted for several uses.
These and other objects will be discerned from a. reading of the following specification taken in connection with the annexed drawing, wherein Figure 1 is a part elevational and part sectional view through the structure when used to blow a whistle.
Figure 2 is a view somewhat like Figure l, but showing the structure arranged to give either or both visual or audible signals at a distance from the device.
Figure 3 is an enlarged view of the lower end of Figure 1.
In the drawing, I is a container preferably made of strong material such as steel, whereby it will withstand the pressure of 500 lbs. per square inch at 70 F., or 6000 lbs. per square inch at 190 F. The container I is adapted to receive a gas or liquid such as carbon dioxide, which I have found to be satisfactory for uses to be described.
One end of the container I has a reduced threaded end 2 and on this is mounted a cup shaped cap 3, having a sleeve portion 4 threaded to engage the threads on the neck 2 of the container I. The cup 5, is formed by the shell 5 and has its bottom I positioned adjacent a seal 8 which is welded to the end of the neck 2. The Seal 8 has a puncturable portion 9 that is adapted to be struck by the piercing point IQ of a hollow pin II. The piercing pin II is fastened as by welding to a plunger I 2, one end of which extends into the cup 5 and has a retaining ring I3 fastened thereto. Also fastened to the plunger I2 is another retaining ring I4, also fastened to the plunger I2 is a disc I 5 that is positioned in spaced relation to another disc I6 that is fastened to the rim of the shell 6. Between the discs I5 and I6 is located material I I that is adapted to fuse at a predetermined point.
Positioned on the disc I B is a gasket I8 preferably of non-metallic material and on this gasket I8 rests a ring I9 which supports a spring which in the form shown is made up of a plurality ,of spring washers 23. The upper one of which is in engagement with the retaining ring I3 so that when the parts are shown in the position in Fig-- ure 1, the spring or its members 2E! are under considerable tension whereby when the material I? is fused at a predetermined temperature, the disc I5 is released and the spring will drive the plunger I2 with the piercing pin II upwardly so that the cutting edge of the pin will strike the. portion 9 of the seal 8 and puncture it, allowing the gas or liquid therein to flow through the hollow pin I I, andto produce a whistle on the member 2! which is attached to the plunger I2. A gasket 22 is utilized between the bottom of the cup I and the seal so as to insure that the gas or liquid of the container I will pass into the hollow pin I I. The gasket 22 has a hole therein somewhat smaller in diameter than the outer diameter of the pin I I so as to further insure passage of the gas or liquid into the hollow pin.
By utilizing a cup 5 having considerable area, and springs of considerable diameter, relatively large radiating surfaces are provided so that the spring or springs will not be damaged by the rise of temperature required to fuse the metal I1. Furthermore, the large radiating surface just described insures that the spring will retain its spring function and hold the plunger 52 against the bottom I of the cup, while the material inside the container I is being extruded through the pin II.
Since the CO2 gas expands very quickly and absorbs a large amount of heat, this tends to keep the pin Ii cool and thereby cools the surrounding air in the cup 5, as well as cooling the spring 29.
In Figure 2, the plunger I2 carries a cylinder 23 in which a piston 24 is located. The piston has a rod 25 connected to a lever 2t through a motion pick-up means 2?. The lever 25 is pivoted at 28 and its end 29 is adapted to engage a contact 30, connected to a relay R supplied with current from battery B. A lamp L and a horn H are adapted to be operated through the relay contact 3| which contact also serves to lock the relay R in operative position under control of the switch S.
Instead of blowing a whistle or horn or light ing a signal lamp, the structure may be used to inflate a membrane or fabric shell which may serve as a signal in some cases.
While in the preceding I have described the structure as one for initiating a signal for alarm purposes, the gas and liquid coming from the container I may be utilized to remove heat from or freeze some material, by voluntarily fusing the metal l1.
In Figure 1, I have shown a hook 32 which may be utilized for hanging the device on a suitable support. The hook 32 may be of the open type or in the form of an eye.
From what has been said, it will be readily understood that certain of the details entering into the construction of my device may be varied without departing frcm the spirit or" my invention and the scope of the depending claims.
Having thus described my invention, what I claim is:
l. A signal control structure comprising a single element container closed at one end by a puncturable seal and containing gas-or liquid under pressure, a cup shaped cap having a sleeve portion with means for attaching it over the end of the container having the seal, a plunger having at least one end extending into the cup part of the cap, retaining rings fastened to the plunger in spaced relation, a support plate fastened to the rim of said cup part, a disc fastened to the plunger adjacent the outer of said retaining rings and spaced a short distance from said support plate, fusible metal normally anchored to both the support plate and said disc, a hollow piercing pin carried by the plunger and extending into a guide hole in the bottom of the cup to a point adjacent said seal and spring means located within the cup and acting on the inner of said retaining rings to force the plunger and pin rapidly toward the seal and cause the pin to puncture the seal when the fusible metal is fused.
2. A signal control structure as defined in claim 1 further characterized in that said piercing pin spring and plunger are so co-related that the pin will puncture the seal before the end of the plunger will hit thebottom of the cup while the spring will have suflicient tension to hold the plunger against the bottom of the cup after said seal has been broken.
3. A signal control structure as defined in claim 1 further characterized in that a ring for supporting the spring is positioned on the inner wall-f the cup adjacent said support plate but preferably separated therefrom by .a heat :resisting gasket.
4. A signal control structure as defined in claim 1 further characterized in that a suitable non-metallic gasket is positioned within the sleeve against the opposite side of the cup bottom, the gasket having a hole therein slightly smaller than the outside diameter of the pierclng pin for the purpose described.
5. A signal control structure comprising a. single element container having an integral much reduced end, closed at said :end by a nonshatterable but puncturable seal and contain-- ing gas or liquid under pressure, means attachable to the reduced end of the container having the seal and carrying a device for'puncturing the seal and directing the flow of the gas or liquid Git therefrom, fusible means for normally holding tially within the hollow plunger, a spring directly connected to the plunger for driving the .plunger and pin into puncturing position to release said gas or liquid through said hollow pin andcmeansjincluding a readily meltable element for holding the plunger pin and spring under restraint 'until a predetermined temperature is reached.
7. A signal control structure comprising a single element container closed at one end by a seal that will withstand a high pressure but having a predetermined puncturable portion and containing gas .or liquid under pressure, means including a readily meltable element for holding a puncturing pin which is hollow uniformly throughout its length adjacent said seal until a predetermined temperature is reached and then releasing it and spring means alone acting solely and directly on the plunger for moving said pin when releasedbysaid meltable element and causing it to strikethe seal so as to surely puncture it and direct the quantity and the flow of the contents of the container from the pumture end of the pin through its entire length thereof and out at its oppositeend for the purpose described.
8. A signal control "structure as defined in claim 5 further characterized in that said at-'- tachable means is a cup shaped member awhile said pin moving means is a plurality of individual spring washers radially spaceda considerable distance from the pin to also act as radiating surfaces for the purpose described.
1-9. A signal control structure which may be subjected to high temperature, comprising a single element container for carrying a mate'- rial which will expand-rapidly when released, a seal at one end of the container, means directly fastened to the container at the 'seal end 'for carrying a hollow pin for puncturing the seal at a :predetermined temperature, said last men tioned means including a plural part spring and disposed so they will be kept sufficiently cool, by said materialin=the containerhwhenit'is released onpuncture of'the'se'al, by flow through said .pin to :insure that said spring parts will function properly until the :mate'rial .is all used up.
FRANK C. WILLIAMS.
REFERENCES CITED The following references are of record in the file of this patent: .UNITED STATES .PA'I ENTS Number Name Date 1,969,880 *Evans et -a1 Aug. 14, 1934 2,166,277 Adams July 18, 1939 "2,410,310 Smith 'Oct. 29, 1946
US751316A 1947-05-29 1947-05-29 Signal control structure Expired - Lifetime US2506983A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US751316A US2506983A (en) 1947-05-29 1947-05-29 Signal control structure

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US751316A US2506983A (en) 1947-05-29 1947-05-29 Signal control structure

Publications (1)

Publication Number Publication Date
US2506983A true US2506983A (en) 1950-05-09

Family

ID=25021459

Family Applications (1)

Application Number Title Priority Date Filing Date
US751316A Expired - Lifetime US2506983A (en) 1947-05-29 1947-05-29 Signal control structure

Country Status (1)

Country Link
US (1) US2506983A (en)

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2590770A (en) * 1950-04-04 1952-03-25 Hirschle Alfred Automatic fire alarm
US2613849A (en) * 1949-06-03 1952-10-14 Prel Inc Cartridge for pressure dispensing devices
US2626586A (en) * 1953-01-27 Fire alarm device
US2649752A (en) * 1952-01-10 1953-08-25 Paul J Showstack Self-contained fire alarm and fire extinguisher
US2682855A (en) * 1950-06-09 1954-07-06 Gerace Jerome Combined illuminating device and fire alarm
US2684180A (en) * 1950-01-10 1954-07-20 C O Two Fire Equipment Co Stored pressure medium container with discharge control
US2719507A (en) * 1953-03-24 1955-10-04 Fenster Personal alarm device
US2764121A (en) * 1954-02-15 1956-09-25 Paul J Showstack Gas alarm device
US2778330A (en) * 1953-05-05 1957-01-22 Evergard Fire Alarm Co Inc Fire alarm
US2802696A (en) * 1953-07-24 1957-08-13 Galeazzi Franco Spray cap and bottle
US2822961A (en) * 1954-06-25 1958-02-11 Nels W Seaquist Aerosol bomb
US2993466A (en) * 1960-04-13 1961-07-25 Robertshaw Fulton Controls Co Alarm device
US3064740A (en) * 1959-10-26 1962-11-20 Knapp Monarch Co Thermal-responsive bulb
US3104384A (en) * 1959-06-04 1963-09-17 Thompson Ramo Wooldridge Inc Alarm system
US4170189A (en) * 1976-12-27 1979-10-09 Falcon Safety Products, Inc. Sensor element and assembly for thermally responsive apparatus
US4635822A (en) * 1984-02-13 1987-01-13 F.P.D. Future Patents Development Company S.A. Apparatus for producing and spraying a mixture consisting of at least two components, e.g. liquids, and a propellant gas
US5110012A (en) * 1991-01-11 1992-05-05 Scholle Corporation Beverage container with regulated pressure
US20030226845A1 (en) * 2002-03-29 2003-12-11 De La Serna Pedro E. Compressed gas cylinder
US20090173506A1 (en) * 2006-05-18 2009-07-09 Hideo Yoshida Fire Extinguishing Gas Spray Device
US20170029081A1 (en) * 2015-03-17 2017-02-02 Bogdan Michalski Modular electronic activation system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1969880A (en) * 1930-04-15 1934-08-14 Merchant And Evans Company Fire extinguisher
US2166277A (en) * 1938-03-09 1939-07-18 Charles L Adams Fire extinguisher
US2410310A (en) * 1944-10-14 1946-10-29 Gen Motors Corp Refrigerating apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1969880A (en) * 1930-04-15 1934-08-14 Merchant And Evans Company Fire extinguisher
US2166277A (en) * 1938-03-09 1939-07-18 Charles L Adams Fire extinguisher
US2410310A (en) * 1944-10-14 1946-10-29 Gen Motors Corp Refrigerating apparatus

Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2626586A (en) * 1953-01-27 Fire alarm device
US2613849A (en) * 1949-06-03 1952-10-14 Prel Inc Cartridge for pressure dispensing devices
US2684180A (en) * 1950-01-10 1954-07-20 C O Two Fire Equipment Co Stored pressure medium container with discharge control
US2590770A (en) * 1950-04-04 1952-03-25 Hirschle Alfred Automatic fire alarm
US2682855A (en) * 1950-06-09 1954-07-06 Gerace Jerome Combined illuminating device and fire alarm
US2649752A (en) * 1952-01-10 1953-08-25 Paul J Showstack Self-contained fire alarm and fire extinguisher
US2719507A (en) * 1953-03-24 1955-10-04 Fenster Personal alarm device
US2778330A (en) * 1953-05-05 1957-01-22 Evergard Fire Alarm Co Inc Fire alarm
US2802696A (en) * 1953-07-24 1957-08-13 Galeazzi Franco Spray cap and bottle
US2764121A (en) * 1954-02-15 1956-09-25 Paul J Showstack Gas alarm device
US2822961A (en) * 1954-06-25 1958-02-11 Nels W Seaquist Aerosol bomb
US3104384A (en) * 1959-06-04 1963-09-17 Thompson Ramo Wooldridge Inc Alarm system
US3064740A (en) * 1959-10-26 1962-11-20 Knapp Monarch Co Thermal-responsive bulb
US2993466A (en) * 1960-04-13 1961-07-25 Robertshaw Fulton Controls Co Alarm device
US4170189A (en) * 1976-12-27 1979-10-09 Falcon Safety Products, Inc. Sensor element and assembly for thermally responsive apparatus
US4635822A (en) * 1984-02-13 1987-01-13 F.P.D. Future Patents Development Company S.A. Apparatus for producing and spraying a mixture consisting of at least two components, e.g. liquids, and a propellant gas
US5110012A (en) * 1991-01-11 1992-05-05 Scholle Corporation Beverage container with regulated pressure
US20030226845A1 (en) * 2002-03-29 2003-12-11 De La Serna Pedro E. Compressed gas cylinder
US7156257B2 (en) * 2002-03-29 2007-01-02 Alza Corporation Compressed gas cylinder
US20090173506A1 (en) * 2006-05-18 2009-07-09 Hideo Yoshida Fire Extinguishing Gas Spray Device
US8651194B2 (en) * 2006-05-18 2014-02-18 Hideo Yoshida Fire extinguishing gas spray device
US20170029081A1 (en) * 2015-03-17 2017-02-02 Bogdan Michalski Modular electronic activation system
US10011332B2 (en) * 2015-03-17 2018-07-03 Bogdan Michalski Modular electronic activation system

Similar Documents

Publication Publication Date Title
US2506983A (en) Signal control structure
US2687541A (en) Apparatus for refloating submerged objects
USRE29614E (en) Rupturing head for fire extinguishers
US3613793A (en) Fire extinguisher system
US2328916A (en) Floating signal
US4011911A (en) Portable fire extinguisher
US3520273A (en) Flare support and release means therefor
US3244137A (en) Pneumatically actuated fire alarm
US1565036A (en) Fire-extinguishing grenade
US3209949A (en) Operating valve with pressure indicating device
US2919833A (en) Means for inflating life saving devices
US2357417A (en) Indicator for locating missing aircraft
US6036559A (en) Flotation device for a submerged article
US2626586A (en) Fire alarm device
US2649752A (en) Self-contained fire alarm and fire extinguisher
US6075450A (en) Audible warning device with restrainable, shock-activated cocked mechanism
US3929091A (en) Automatically inflating and liberating a balloon
US1939333A (en) Fire extinguisher
US1969880A (en) Fire extinguisher
US3061148A (en) Inflatable bag
US648371A (en) Fire-extinguisher.
US701329A (en) Automatic self-inflating life-preserver.
US3896278A (en) Freezer monitor thermal responsive switch with gravity actuated plunger contact retained by freezable liquid in open switch position
US2764121A (en) Gas alarm device
US2708895A (en) Fire alarm device