Overhead socket smoke detector with theft alarm

An overhead socket smoke detector with a theft alarm includes a case with a bulb base at one end and a lamp socket at an opposite end and connected to the bulb base by a socket switch which is closed by a lamp received in the socket to electrically activate the socket. The case has a cylindrical diameter to fit within a can light fixture. Smoke alarm circuitry is mounted within the case and includes a smoke sensor circuit, a trigger circuit, and a sounder circuit. A unit removal or theft switch connected to the trigger circuit includes a switch operator extending through the bulb base to engage a socket into which the case is threaded. A rechargeable battery and a battery charger are connected between the bulb base and the alarm circuitry and provide power to operate the alarm circuitry. When the unit is removed from its fixture, the unit removal switch disengages the fixture socket and triggers the sounder circuit into activation to deter removal of the unit from the socket in which it is mounted.

FIELD OF THE INVENTION 
The present invention relates to smoke detector devices and, more 
particularly, to such a device which is powered by a rechargeable battery, 
which is adapted for threaded reception in an overhead light socket and 
receiving a lamp bulb therein, and which includes a theft removal switch 
which triggers the alarm when the unit is removed from the light socket. 
BACKGROUND OF THE INVENTION 
Fire and smoke detector devices have been developed to alert occupants of 
rooms and buildings to take emergency action in the earliest stages of a 
fire. In many localities, ordinances have been enacted requiring the 
installation of smoke detector devices in all new and existing dwellings. 
Smoke alarm devices are available as battery powered units and as AC 
powered units. Permanently wired AC powered units are generally more 
expensive to purchase and usually require the services of an electrician. 
Battery powered smoke alarms are inexpensive and easy to install, although 
their effectiveness can be diminished by improper placement. 
Battery powered units usually incorporate circuitry which causes a chirping 
signal or the like to be emitted when battery power drops below a 
threshhold level. Some units become unstable and emit false alarms when 
battery power drops to a level just above the threshhold. As a result, 
some residents consider smoke alarm devices to be a nuisance and fail to 
replace exhausted batteries, thus relinquishing the protection afforded by 
them. Battery powered smoke alarm devices, because of their low 
installation costs, are often provided in public housing units. A 
particular problem in such environments is that the units are often 
stolen. 
In general, fire safety experts recommend that smoke alarm devices be 
placed near the ceiling of a room, and preferably near the center. In 
somewhat older homes, such a position is usually occupied by an existing 
light fixture. In newer homes without such ceiling fixtures, there are 
sometimes aesthetic objections to the placement of conventional smoke 
alarm devices in the center of a ceiling. In order to fulfill the needs of 
such circumstances, smoke alarm devices have been developed which 
incorporate light fixtures therein. Because of their use as light fixtures 
which will be switched on and off in the normal course of use, such 
devices are often powered by rechargeable batteries which are charged when 
the lamp is switched on. Smoke alarm devices with combined light fixtures 
are provided as hard wired, permanently mounted fixtures. These are 
suitable for a room with no ceiling fixture or as a replacement for an 
existing light fixture. However, they require professional installation. 
Other types of smoke alarms with light fixtures include an integral 
threaded bulb base at one end for installation in an existing screw socket 
and a unit socket at the other end to receive a lamp bulb. A problem with 
the known devices of this type is that they retain the well known size and 
shape of conventional battery powered smoke detectors, that is, a 
flattened cylindrical shape of about six inches or greater in diameter. 
Devices of this shape are inappropriate for many existing fixtures since 
the alarm devices do not accommodate the diffusers or shades which form a 
part of the existing fixture. Thus, the resident is left with a bare bulb. 
Additionally, modern residential lighting often includes lamps mounted in 
so-called can light fixtures and track light fixtures. The dimensions of 
the broad cylindrical screw-in smoke alarms conventionally available will 
not fit within such fixtures. A problem with both permanently mounted and 
screw-in smoke alarms incorporating lamp sockets is that an electrical 
shock hazard exists in them when no lamp bulb is present in the unit 
socket. 
SUMMARY OF THE INVENTION 
The present invention provides a screw-in smoke alarm device with a lamp 
socket which is deactivated when the lamp bulb is removed and which 
includes a unit removal switch connected to trigger the alarm if the unit 
is removed from the socket in which it is installed. The device includes a 
cylindrical case which is sized to fit within a can light fixture or the 
like and allow adequate airflow therearound to reliably monitor for the 
presence of smoke. A threaded bulb base is provided at one end and a unit 
socket at the opposite end. A socket switch connects the unit socket to 
the bulb base and is closed to activate the unit socket only if a lamp 
bulb is threaded into it. 
Conventional smoke, or alternatively heat, alarm circuitry is positioned in 
the case and includes a smoke or heat sensor, a trigger circuit, and a 
sounder circuit. The circuitry is powered by a rechargeable battery which 
is maintained by a charger circuit receiving power from the existing 
socket in which the unit is installed when the existing socket is 
electrically active. A unit removal, or theft, switch is connected to the 
trigger circuit and includes a button or switch operator which extends 
through the bulb base to engage the fixture socket. Once the unit has been 
installed in the fixture socket and the battery has been charged, removal 
of the unit from the fixture socket releases the theft switch operator 
which causes the trigger circuit to activate the sounder circuit and emit 
an audible alarm. The theft alarm is provided to deter removal of the unit 
from its fixture socket. 
The device of the present invention otherwise operates in the manner of a 
conventional smoke or heat detector and allows use of the fixture in which 
it is installed to be operated as a conventional switched light fixture. 
OBJECTS OF THE INVENTION 
The principal objects of the present invention are: to provide an improved 
smoke alarm device; to provide such a device which incorporates a light 
fixture therein; to provide such a device which is sized, shaped, and 
otherwise suitable for use with existing types of light fixtures with 
threaded sockets, such as conventional surface mounted fixtures on 
ceilings, can light fixtures, track light fixtures, and the like; to 
provide such a device including a threaded bulb base at one end connected 
to an integral threaded unit socket at the opposite end by a socket switch 
which allows the unit socket to be activated only if a lamp bulb is placed 
in the unit socket; to provide such a device including a theft alarm to 
deter removal of the unit from the socket in which it is installed; to 
provide such a device including a unit removal switch connected to a 
trigger circuit within the unit and a switch operator which normally 
engages the fixture socket in which the unit is installed and which 
disengages therefrom upon removal of the unit and causes the alarm sounder 
to emit an alarm sound; to provide such a device including a rechargeable 
battery for powering the alarm circuitry of the device; to provide such a 
device including a battery charger within the unit, connected to the bulb 
base, receiving power therefrom when the socket in which the unit is 
mounted is activated, and providing charging current to the battery; to 
provide such a device which is easily installable by a resident in an 
existing ceiling light fixture; and to provide such an overhead smoke 
detector with a theft alarm which is economical to manufacture, stable and 
reliable in operation, and which is particularly well adapted for its 
intended purpose. 
Other objects and advantages of this invention will become apparent from 
the following description taken in conjunction with the accompanying 
drawings wherein are set forth, by way of illustration and example, 
certain embodiments of this invention. 
The drawings constitute a part of this specification and include exemplary 
embodiments of the present invention and illustrate various objects and 
features thereof.

DETAILED DESCRIPTION OF THE INVENTION 
As required, detailed embodiments of the present invention are disclosed 
herein; however, it is to be understood that the disclosed embodiments are 
merely exemplary of the invention, which may be embodied in various forms. 
Therefore, specific structural and functional details disclosed herein are 
not to be interpreted as limiting, but merely as a basis for the claims 
and as a representative basis for teaching one skilled in the art to 
variously employ the present invention in virtually any appropriately 
detailed structure. 
Referring to the drawings in more detail: 
The reference numeral 1 generally designates an overhead socket smoke alarm 
device with a theft switch which embodies the present invention. The 
device or unit 1 generally includes a case 2 housing smoke alarm circuitry 
3 (FIG. 4) and having a threaded bulb base 4 at a top end and a threaded 
unit socket 5 at an opposite end. The unit 1 is provided with a unit 
socket switch 7 connecting the unit socket 5 with the bulb base 4 and a 
unit removal switch 8 (FIG. 4) including a removal switch operator 9 which 
extends from the bulb base 4 to engage a fixture socket 10 in which the 
unit 1 is installed. The unit socket switch 7 is a safety provision which 
causes the unit socket 5 to be electrically continuous with the bulb base 
4 only when a lamp 11 is placed in the unit socket 5. The unit removal or 
theft switch 8 is connected to the alarm circuitry 3 and causes an alarm 
sounder 12 (FIG. 4) to be activated when the unit 1 is removed from the 
fixture socket 10. 
Referring to FIGS. 1-3, the case 2 includes a cylindrical portion 14 with a 
frustoconical portion 15 connecting between the cylindrical portion 14 and 
the bulb base 4. The portions 14 and 15 are provided with vents or 
openings 16 to allow the flow of air through the case 2 to allow the 
circuitry 3 to monitor it for smoke particles. The cylindrical portion 14 
is the widest part of the unit 1 and has a diameter which is only slightly 
greater that the principal axial diameter of the low to medium wattage 
light bulb 11. Thus, the unit 1 is sized to fit within standard sizes of 
can light fixtures 18, shown diagrammatically in FIG. 2, and similar types 
of fixtures, with adequate room around the case 2 to allow the flow of air 
through the fixture 18. 
Referring to FIG. 4, the unit 1 incorporates conventional types of alarm 
circuitry 3, which may either be for the detection of smoke or excessive 
levels of heat. The unit 1 is described herein principally with reference 
to smoke detection; however, with the exception of the type of sensor 
used, the circuitry 3 is also suitable for heat detection. The illustrated 
circuitry 3 includes a smoke sensor 20, with an alternative heat sensor 21 
shown in phantom, an alarm trigger circuit 22, an alarm driver circuit 23, 
and the alarm sounder 12. 
The smoke sensor 20 may be a conventional ionization type smoke sensor, a 
photoelectric type smoke sensor, or the like. The heat sensor 21 may be a 
thermovoltaic device or may incorporate a thermistor or a temperature 
dependent transistor of conventional design. The sensors 20 and 21 may be 
referred to generically as thermal emergency sensors 25 and provide a 
thermal condition signal proportional in some manner to the smoke particle 
content or temperature of air flowing through the case 2. 
The trigger circuit 22 is a threshhold or comparator type of circuit to 
which the sensors 25 are connected and which compares the level of the 
condition signal therefrom with a reference signal. When the condition 
signal level equals or exceeds the reference signal, the trigger circuit 
22 outputs a trigger signal, which may be either analog or digital in 
form, until the condition signal level drops below the reference level. 
The alarm driver circuit 23 responds to the trigger signal by activating 
the sounder 12 to emit an alarm sound signal as long as the trigger signal 
is present. The sounder 12 may be a solid state type of audible signalling 
device. Such devices are well known and are capable of emitting a loud, 
shrill sound which is difficult for most persons to ignore. The unit 1 
preferably includes a test switch 26 which is connected to the trigger 
circuit 22 and which may include a timer (not shown) whereby pressing a 
test button 27 (FIGS. 1 and 3) causes the trigger circuit 22 to output the 
trigger signal for a selected length of time to test the alarm sounding 
operability of the unit 1. 
The alarm circuitry 3 of the unit 1 is powered by a rechargeable battery 
29, which may be a nickel-cadmium battery or the like. The battery 29 is 
recharged by a battery charger circuit 30 which, along with the battery 
29, is mounted within the case 2. The charger 30 is connected across the 
conductors of the bulb base 4 and receives power from the fixture socket 
10 through the bulb base 4 when the socket 10 is switched to electrical 
activation by completing a circuit with a power line 32 connected thereto 
to illuminate the bulb 11. 
The unit removal switch 8 is connected to the alarm trigger circuit 22 and 
functions in a manner similar to the test switch 26 except that the 
removal switch 8 does not incorporate a timer therein. The switch 8 has a 
mounted switch state when the removal switch operator 9 is pressed in by 
installation of the unit 1 in the fixture socket 10. When the operator 9 
extends upon removal of the unit 1 from the socket 10, the switch 8 is 
placed in a removed switch state which causes the trigger circuit 22 to 
output the trigger signal for as long as the operator 9 remains out or 
until the battery 29 is exhausted. The trigger signal is accompanied by a 
sound signal from the sounder 12 and, thus, draws attention whenever the 
unit 1 is removed from its installation in the fixture socket 10. 
FIG. 5 illustrates structural details of the removal switch operator 9 and 
the unit socket switch 7 and their relationship to the bulb base 4 and the 
unit socket 5. The bulb base 4 includes a threaded conductive, cylindrical 
neutral terminal 36 which is closed by an end wall 37. An insulator 
grommet 38 is positioned centrally through the wall 37 and has the removal 
switch operator 9 slidably mounted therethrough. The switch operator 9 is 
formed of a conductive metal and forms a hot terminal 39 of the bulb base 
4. The operator 9 has a retainer washer 40 positioned on a shaft 41 
thereof to limit sliding movement of the operator 9. A compression spring 
42 is positioned between a head 43 of the operator 9 and the grommet 38 
and resiliently urges the operator 9 to an extended position. 
The unit socket 5 includes a threaded cylindrical, conductive neutral 
terminal 46 which is closed at one end by an end wall 47. An insulative 
grommet 48 is mounted centrally through the end wall 47 and has a 
conductive rivet 49 therein which forms a hot terminal of the unit socket 
5. A hot connector lug 50 may also be retained by the rivet 49. A second 
insulative grommet 51 is mounted through the end wall 47 at a radially 
outward position therefrom, and a second rivet 52 retains a spring 
conductive contact 53 within the unit socket 5. The contact 53 extends 
over a lower end of the rivet 49 and is resiliently urged away therefrom. 
The center rivet 49 and the spring contact 53 form contacts of the unit 
socket switch 7 which is a normally open switch. 
The neutral terminal 36 of the bulb base 4 is connected to the neutral 
terminal 46 of the unit socket 5 by a neutral conductor 56. The hot 
terminal 39 or switch operator 9 of the bulb base 4 is connected to the 
lug 50 on the rivet 49 of the unit socket 5 by a hot conductor 57. Thus, 
when the unit 1 is positioned in the fixture socket 10 and it is 
electrically active, accessible conductors of the unit socket 5 are not 
electrically active and do not present a shock hazard. The accessible 
contact 53 is not electrically activated until the bulb base 60 of the 
lamp bulb 11 is threaded into the unit socket 5 and the hot terminal 61 of 
the bulb base 60 presses the contact 53 into conductive engagement with 
the center rivet 49. 
The unit removal switch 8 is illustrated in FIG. 5 as a push button switch 
unit which is mounted within the bulb base 4 and which includes an 
operator button 63 aligned with the shaft 41 of the operator 9. This 
allows the unit removal switch 8 to be electrically isolated from the AC 
power levels carried by the operator 9 which functions as the hot terminal 
39 of the bulb base 4. Alternatively, other types of switch units or 
switch contact arrangements which accomplish the same purpose could be 
provided in the unit 1. The unit removal switch 8 may be either a normally 
open switch or a normally closed switch (in its extended position) 
depending on the logic requirements of the alarm trigger 22 to which it is 
connected. 
The removal switch operator 9 engages a hot terminal (not shown) of the 
fixture socket 10 when the unit bulb base 4 is threaded thereinto. This 
places the unit removal switch 8 in its mounted switch state, which causes 
the trigger circuit 22 to respond only to the sensor 25 or the test switch 
26. When the unit bulb base 4 is unthreaded from the fixture socket 10, 
the operator 9 extends and places the removal switch 8 in its removed 
switch state which causes the trigger circuit 22 to output its trigger 
signal to thereby activate the sounder 12. 
It is to be understood that while certain forms of the present invention 
have been illustrated and described herein, it is not to be limited to the 
specific forms or arrangement of parts described and shown.