Patent ID: 6317043
Filing Date: 2001-11-13
Classification: G08B

Abstract:
A perimeter monitoring system comprising:a. a reflector positioned to receive a beam of light along a segment of a perimeter of an area to be monitored and to provide a returned beam along the segment, the returned beam comprising a pulse modulation having a pulse repetition period;b. a monitor comprising:(1) an emitter that provides the beam;(2) a detector having an axis, the detector providing a signal comprising indicia of a lapse in detecting the returned beam, the detector comprising a blocking device that blocks detection of light not received through a passage having an aperture, wherein the aperture has a diameter and the passage has a length, a ratio of the diameter to the length being less than 0.1;(3) an opaque partition between the emitter and the detector;(4) an enclosure that encloses the emitter and the detector, the enclosure comprising a surface that passes the beam and the returned beam through the surface, the surface oriented to direct a reflected portion of the beam away from the axis; and(5) a timer that provides an alert signal on lapse of a time greater than the period, the timer being retriggered in response to the signal;c. transmitter that transmits light in response to the alert signal; andd. a remote alarm comprising a receiver and an alarm, wherein the receiver activates the alarm in response to receiving the transmitted light.