Burglar alarm device

Details Burglar alarm device Burglar alarm device

1977-03-24

1981-06-23

Caldwell, Sr., John W.

Communications: electrical

Condition responsive indicating system

Specific condition

343 5PD, 343 6R, 343 77, 367 94, G08B 1316, G08B 1318, G08B 2900

Patent

active

042753902

ABSTRACT:
Burglar alarm apparatus includes an ultrasonic transmitter and an electromagnetic radiation transmitter whose signals are Doppler frequency shifted by an object moving through the radiation fields, the signals being received by respective demodulating receivers which provide respective electrical signals corresponding to the Doppler frequency. Frequency conversion apparatus is connected to one of the receivers to convert the output frequency thereof by a predetermined ratio to normalize or equalize the frequencies and a signal comparison circuit is provided to produce a signal in response to a ratio of the Doppler shifted signals within a predetermined tolerance range.

REFERENCES:
patent: 3074053 (1963-01-01), McDonough et al.
patent: 3074054 (1963-01-01), Pearson
patent: 3727216 (1973-04-01), Antonio
patent: 3778823 (1973-12-01), Sato et al.
patent: 3801978 (1974-04-01), Gershberg et al.
patent: 3846778 (1974-11-01), Galvin et al.

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