Abstract An alarm system for protection against unauthorized intrusion which comprises a closed electric circuit and an alarm responsive to a break in said closed circuit and further comprising a fourleg bridge circuit wherein each leg of the bridge comprises a different resistive portion of said closed circuit or comprises a nonresistive value to balance any part or all of an unused leg of said bridge. A plurality of high gain amplifiers are each associated with a different pair of legs of said bridge circuit and each amplifier is attached to detect a change in the resistive value of said leg pairs and to produce a current in response to said change, which current actuates said alarm. This alarm system makes virtually impossible the compromising of the alarm system by shunting any terminals of any switch, actuator, connecting leads, or entrance or exit terminals of any surface to be protected.
Inventors
👤 John W Walter
Bibliographic Details
Application Number—
JurisdictionUS
Data Sourcegoogle_patents
Last Synchronized2026-10-25 00:04
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/02; G08B13/04
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
116 words
An alarm system for protection against unauthorized intrusion which comprises a closed electric circuit and an alarm responsive to a break in said circuit, further comprising: a pair of two-leg resistance bridge circuits wherein a different resistive portion of said closed electric circuit is comprised in one or more legs of said resistance bridge circuits so that initially each leg of said resistance bridge circuits is of equal resistance, and a plurality of high gain amplifiers each associated with a different pair of legs of said resistance bridge circuits; to detect a change in the resistive value of said leg pairs and to produce a current in response to said change which current actuates said alarm.
Claim 2
Dependent Claim
116 words
An alarm system for protection against unauthorized intrusion which comprises a closed electric circuit and an alarm responsive to a break in said circuit, further comprising: a pair of two-leg resistance bridge circuits wherein a different resistive portion of said closed electric circuit is comprised in one or more legs of said resistance bridge circuits so that initially each leg of said resistance bridge circuits is of equal resistance, and a plurality of high gain amplifiers each associated with a different pair of legs of said resistance bridge circuits; to detect a change in the resistive value of said leg pairs and to produce a current in response to said change which current actuates said alarm.
Claim 3
Dependent Claim
42 words
An alarm system according to claim 1 wherein at least one resistive portion of said closed circuit comprises a resistor which is hidden across the terminals of a switch and wherein said switch is adapted when opened to shunt out said resistor.
Claim 4
Dependent Claim
28 words
An alarm system according to claim 2 wherein said switch is adapted when opened first to break said closed electrical circuit and then to shunt out said resistor.