Patent attributes
A security sensor system includes beam projecting and receiving units (1) and (2). The proper range of the received beam level is adjusted with change in time of the received beam level so that in the case that the received beam level departs from the proper range, the amount of beam projected from the beam projecting unit (1) can be adjusted to enable the received beam level to fall within the proper range. The unit (2) includes a received beam level detector (27), a level setting circuit (28) for setting a proper range of the received beam level, a request signal output circuit (30) for outputting a request signal requesting an adjustment of the amount of beam, and a transmitter (33) for transmitting the request signal to the unit (1). The unit (1) includes a beam projecting power adjustor (15) operable in response to the request signal.
