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US 4,853,677 AGranted
Portable intrusion alarm
OwnerAlfred E. Yarbrough, Jerry O. Ballinventors
Life of this patent
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Abstract
An intrusion alarm system, for an enclosed space responsive to frequencies in the one to two Hertz range for detecting opening of doors or windows; and responsive to frequencies in the three to four Khz range for detecting breaking glass. A detected frequency in the one to two Hertz range increases the sensitivity required for detecting breaking glass.
Claims13
An intrusion alarm system, comprising:
- a microphone operative to detect changes in ambient atmospheric pressure;
- low frequency filter means responsive to the detected ambient pressure changes operative to generate an output at times when the frequency of the pressure changes correspond to the opening of either a door or window;
- first circuit means responsive to the output of the low frequency filter means operative to generate a first output signal upon the detected pressure changes reaching a first predetermined threshold;
- high frequency filter means responsive to the detected atmospheric pressure changes operative to generate an output at times when the frequency of the detected pressure changes correspond to the sound of breaking glass;
- second circuit means responsive to the output of the high frequency filter means operative to generate a second output signal upon the detected pressure changes reaching a second predetermined threshold;
- sensitivity circuit means responsive to the output of the low frequency filter means for decreasing effectively the second predetermined threshold;
- and
- alarm circuit means responsive to either one of the first and second output signals for generating a discernible alarm.
5 more elements
An intrusion alarm system, comprising:
- a microphone operative to detect changes in ambient atmospheric pressure;
- low frequency filter means responsive to the detected ambient pressure changes operative to output signals having frequencies within a selected range;
- first circuit means responsive to the output of the low frequency filter means operative to generate a first output signal upon the detected pressure changes reaching a first selected threshold;
- high frequency filter means responsive to the detected atmospheric pressure changes operative to generate an output at times when the frequency of the detected pressure changes correspond to the sound of breaking glass;
- second circuit means including capacitance means responsive to a plurality of successive outputs of the high frequency filter means operative to generate a signal indication of breaking glass, said high frequency circuit means being operative to generate a second output signal in response to the break signal reaching a level corresponding to a second predetermined threshold;
- sensitivity circuit means responsive to the output of the low frequency filter means for decreasing the effective level of the second predetermined threshold;
- and
- alarm circuit means responsive to either one of the first and second output signals for generating a discernible alarm.
5 more elements
Dependencies are inferred from the claim text.