Device for protecting components of security systems against obs

Details Device for protecting components of security systems against obs Device for protecting components of security systems against obs

1991-10-15

1993-09-07

Peng, John K.

Communications: electrical

Condition responsive indicating system

Specific condition

250221, 34030915, 340693, G08B 1318

Patent

active

052433269

ABSTRACT:
An element of an intrusion-alarm system, for example a passive infra-red sensor, has two subsystems which protect it against obstruction. The first subsystem can detect attempts at obstruction by the removal of the lens or front screen of the element or by the spraying of the element with a spray or a lacquer. The second subsystem projects, towards the area under surveillance, radiation which can be reflected by a masking screen. The detection of this reflected radiation gives rise to the emission of a warning signal.

REFERENCES:
patent: 4797548 (1989-01-01), Kobbing et al.
European Search Report; Appln. No. EP 91 83 0439.

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