Importance

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Abstract

An alarm device responsive to entering or trespassing comprising: (a) a sensor circuit, including an infrared ray sensor, producing an output having positive and negative peaks based on outputs of said sensor being produced when a target to be sensed passes within the region of vision monitored by said sensor, (b) a level detecting circuit comprising a first detector producing an output when the positive peak of the output fed from said sensor circuit exceeds a predetermined level, and a second detector producing an output when the negative peak of the output fed from said sensor circuit exceeds a predetermined level, (c) a timer circuit comprising a first timer producing an output which continues for a predetermined time interval or above from a time at which the output of said first detector is produced, and a second timer producing an output which continues for a predetermined time or above from a time at which the output of said second detector is produced, (d) an AND circuit comprising a first circuit producing an output when there exist the output of said first timer and the output of said second detector at the same time, and a second circuit producing an output when there exist the output of said second timer and the output of said first detector at the same time, and (e) an output circuit responsive to the output of said AND circuit to produce an alarm signal.

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First Claim