US2921299A - Alarm system - Google Patents

Description

Jan. 12, 1960 B, Z|MMERMAN 2,921,299

ALARM SYSTEM Filed'Feb. 10, 1958 FIG 2.

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ALARM SYSTEM Benjamin E. Zimmerman, Conger-ville, Ill.

Application February 10, 1958, Serial No. 714,247

2 Claims. (Cl. 340-274) This invention relates to protective devices for locks. While it has particular application to alarm systems for automobile ignition switch locks, its application is not limited thereto.

The enormous number of car thefts in the United States each year, is a matter of common knowledge. It is desirable both to make such thefts difficult, and to apprehend those who are predisposed to steal automobiles. The problem is not a new one. A patent to Stone, No. 1,351,973, issued September 7, 1920, discloses a device in circuit withthe ignition switch of a motorvehicle, whereby an alarm is sounded if the ignition switch is tampered with. The Stone device, and that of Lodispoto, No. 2,011,944, issued August 20, 1935, depends upon, the movement of tumblers within the ignition lock, the insertion of a false key leading 'to the setting off of an alarm. However, the use of false keys has lost its vogue among modern car thieves, who use jumpers, unless the owner leaves the key in the ignition.

One of the objects of this invention is to provide a simple, eifective device for discouraging tampering with locks.

Another object is to provide an alarm devicewhich is likely to be actuated by one attempting to operate the lock without authority.

Still another object of this invention is to provide an alarm device which will continue to operatefor a predetermined length of time after it is started, even though the lock be returned to its original position, and which will reset itself automatically.

Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.

In accordance with this invention, generally stated, an alarm device is provided for a key operated lock, which alarm device is operated by the use of a false key Whichis deliberately inserted in the lock when the lock is to be left unattended. The presence of the key encourages the would-be thief to use it, rather than using a jumper or otherwise bypassing or jimmying the lock. The false key is arranged to trip a device which sounds an alarm for a predetermined length of time, Whether the false key is returned to its original position or not. At the end of that predetermined time, if the false key has been returned to its original position, the alarm will shut off and the device will reset itself automatically. If the key is not returned to its original position, the alarm will continue to sound.

In the drawing,

Figure 1 is a somewhat diagrammatic view in side elevation, partly in section, of a device constructed in accordance with one illustrative embodiment of this invention;

Figure 2 is a sectional view taken along the line 2-2 of Figure 1; and

Figure 3 is a view in side elevation of an operating key.

v United States Patent F Patented Jan. 12, 1960 Referring now to the drawing for one illustrative embodi.nent of this invention, reference numeral 1 indicates a tumbler-type lock, adapted to be operated by a key 2. A false key 3 is designed to fit into the lock 1, but is provided with an extension or tab 6 which, when the key 3 is'in place in the lock, projects beyond the tumblers and into a slot 8 in a disc 10 of an alarm device. In this embodiment, the dotted disc is the operating mechanism.

The disc 10 is mounted for rotation. In the diagrammatic view shown in Figure l, the disc 10 is mounted on a post 12 secured to a base 14, The disc 10 has a cam 16 projecting from itsperiphery. The cam 16 engages the underside of a contact bar 20, which is pivoted on a pivot pin 22. The pivot pin 22 extends diametrically through a hollow post 24. The bar 20 extends through the hollow post 24 diametrically, at right angles to the pin 22. To this end, slots 26 are provided in the hollow post 24, through which the bar 20 extends. Within the hollow post 24, below the bar 20, is a coil spring'30, compressed between the underside of the bar 20 and the top of the base 14. An upper spring 32 is compressed between the top side of the bar 20 and a threaded plug 34 in the hollow post 24. The springs 30 and 32 are loosely enough confined 'within the hollow post 24 to serve as overcentering devices. In the position of the bar 20 shown in solid lines in Figure 1, upper spring 32 is shifted to the right of the pivot 22 and lower spring 30 is shifted to the left of the pivot, as viewed in that figure, in which positions they bias the bar 20 to a position with its right end depressed and its left end elevated from the horizontal. When the right end of the bar 20 is elevated against the bias of the springs 30 and 32 until the right end of the bar 29 is above the horizontal and left end of the bar 20 is below the horizontal, the positions of the springs 30 and 32 are reversed, with the upper spring 32 displaced to the left of the pivot and the lower spring 30 displaced to the right of the pivot, as viewed in Figure 1. Under these circumstances, the bar 20 will be maintained in the postion shown in dotted lines in Figure 1, untilit is moved against the bias of the springs 30 and 32 to restore it tothe position shown in solid lines in Figure 1.

Mounted on the base 14 on the opposite end of the base from the disc 10, with respect to the post 24, are a contact bracket 40 and a resetting device 50.

The contact bracket 40 has an adjustable contact 41.

The resetting device 50,-shown somewhat diagrammatically in Figure 1, has a bimetallic strip 51 mounted on a spool 52 of refractory material. A heating element 53 isshown as wound on therefractory spool 52,,and connected electrically to the bimetallic strip 51. The bimetallic strip 51 carries an adjustable contact 54. The bimetallic strip 51 is normally elliptical, as shown in solid lines in Figure 1, but has the property of becoming circular when heated and free to move, as indicated by dotted lines in Figure 1.

In this embodiment, the bar 20, contact bracket 41) and resetting device 50 are all parts of an electrical circuit 60, which also includes a power source 65 and an alarm device 70. The power source 65 may be any suitable and convenient power source. In an automobile, it will be the battery. The alarm device 70 may take the form of lights, horn, bells, or any other suitable visual terial. However, asispointed outhereafter,thisarran ment is merely illustrative.

The heating element 53, hence the bimetallic element is c nnec ed byr con uctor 67 10.-the n ga ive si of h PQ nsQum hS. 'Ih alarm d v eefl l iislalso connected, i ser s wi t e cont t b a k t :tout conductor 6'], hence to the negative side of gtherpower source.

In operation, if the ope ating ikey 2 -is inserted in the lock, it extends, as indicated in dotted lines in Figure 2, far enough to operate the lock, but not far enough to reach the disc 10. Accordingly, the alarm apparatus remains unaffected by theturning of the key.

When the false key 3 is in position, however, ;the'tab 6, extending through ,theslot 8, operates to rotate the disc 10 when thekey 3,'is turned. Stops, not here shown, serve to prevent the jalse keys being turned ,far enough to operate the lock. Therotation of the disc,10 causes the cam 16 to move the bar 20 to the position shown in dotted lines in Figure 1. This causes the springs 30 and 32 to move over center, to maintain the bar .20 in the position shown in dotted lines, even though the key 3, hence the disc 10, is restored to its original position. With the bar 20 in the position shown in dotted lines, it makes contact with the adjustable contact 4110f the contact bracket 40, and with the adjustable,contact,,54 of the bimetallic strip 51. This completes a circuit from the positive side of the power source 65, hrough the bar 20, contact 41, contact bracket 40, alarm device 70, and conductor 67 to the negative side of the power source; and through the bar 20, contact 54, bimetallic strip 51, heating element 53 and conductor '67 to the negative side of the power source 65. The efiect of the completion ofthese circuits is to cause the alarm deviceto operate, and at the same time to start the heating of the heating element 53, which heats the bimetallic strip .51, tending to cause it to assume the circular configuration shown in dotted lines in Figure 1. If the key 3 has not been turned back to its original position, the cam 16 willmaintain the bar 20, against the bias of the bimetallic strip 51, in contact with the contact 41, allowing. the alarm device to continue to operate. If the key 3,has been returned to its original position, the heating of the bimetallic strip 51 will cause the bar 20 to, be raised above the horizontal, at whichtime the springs 30 and 32 will reverse their positions and restorethe bar 20 to its initial position. In its initial position, the bar ,20is out of contact with the contact 54 of the bimetallic strip 51, even in the circular position of that bimetallic strip, so that when the springs30 and 32 move over center, they break the contact between the bar 20 and the heating element 53, permitting the bimetallic strip to cool and to return to its original elliptical condition. It can be seen that by regulating the strength of the springs 30 and 32, and by providing suitable heating elements 53, the length of time during which the alarmdevice will .beoperated, when the key ,3. is immediately restored .to-its original position, can be made of any desired duration.

Numerous variations in the construction of the alarm device of this invention, within the scope of the appended claims, will become apparent to those skilled in the art in the light of the foregoing disclosure. For example, it is not at all necessary for the bar 20 to be made of electrically conducting material. The bar may be made of a non-conductor, carrying contacts connected with the conductor 66. Other over-centering devices may be employed, and otherrestoring or resetting means, such, for example, as a timer-actuated resilient biasing means, .althoughthe means specifically described have advantages in simplicity and cheapness. To earns 16 may be provided on the disc'-10,so that the-key'qnay be turned in either direction to raise the bar 20, and a member of difierent shape may be substituted for the disc.

A spring may be attached to the disc 10, to restore it immediately to its neutral position when the key 3 is released. A switch may be provided in the circuit 60, or a device for restoring the bar 20 to its off position may be provided, to permit the alarm to be turned off,

1 if desired.

Thus it can beseen that a simple, dependable device isprovided for discouraging tampering with .locks, and for facilitating the apprehension of tamperers.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. An alarm device for a lock operated by a key, comprising a false keyadapted to fit the lock, said key having altab projecting beyond said lock, an operating mechanism engaged by said tab, a contact bar arranged to be rocked by said operating mechanism to operative position,,over-centering means adapted to bias said contact-barin either operative or inoperative position, resetting means actuated, upon movement of said contact bar, to operative position, to bias said contact bar to inoperative position counter to the bias of the overcentering means, an, electric power source electrically connected on one side with said contact bar, an alarm device connected with the other side of said power source, and contact means connected with said alarm device and positioned to make electrical contact with said contact bar when said contact bar is in operative position.

2. The device of claim 1 wherein the resetting means comprises a bimetallic strip adapted to move when heated to contact-bar biasing position, and a heating element connected with one side ofthe power source and adapted to be connected to the other side of said source when the contact bar is moved to its operative position.

References Cited in the file of this patent UNITED STATES PATENTS

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