Automatic doorbell

Details Automatic doorbell Automatic doorbell

1977-12-09

1980-11-25

Caldwell, Sr., John W.

Communications: electrical

Condition responsive indicating system

Specific condition

340384E, G08B 300, G08B 1318

Patent

active

042361478

ABSTRACT:
Microwave transmitting means, receiving means, and detector means such that the change in the standing wave pattern surrounding said transmitting means caused by the approach of a person on one side of said transmitting means can be detected and distinguished from the approach of a person on the other side, and tone generator means such that an audible tone is generated when a person approaches from one side, but not when a person approaches from the other, adaptable for use as an automatic doorbell.

REFERENCES:
patent: 3237191 (1966-02-01), Bojko
patent: 3300768 (1967-01-01), Bystrom et al.
patent: 3497995 (1970-03-01), Forsberg
patent: 3747109 (1973-07-01), Corbell et al.
patent: 3815130 (1974-06-01), Hayo
patent: 3981007 (1976-09-01), Cieslak et al.
patent: 4001817 (1977-01-01), Squires
patent: 4087814 (1978-05-01), Spirig

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