Passive remote photoelectric surveillance alarm with telescopic optics

摘要

An intruder alarm includes a circuit with a photoresistive cell located in a housing with a piezoelectric crystal sound generator and battery to power the circuit and sound generator. A telescope concentrates light from a distance in a limited field of view upon the photoresistive cell to trigger the piezoelectric crystal sound generator when light intensity on the cell changes sufficiently from an ambient light intensity level.