Abstract: A compound-eye crime prevention sensor system is constructed which reliably distinguishes between a human being and a small animal irrespective of the distance from the detector. This system has a zone spacing changer, and when the detection zones A and B of the detector 1 are at the farthest point L in the trespassing subject detecting range, the spacing between the detection zones A and B is .theta.L and when the optical unit in the detector 1 is rotated to bring the detection zones to the position of a point S, the spacing .theta.S between the detection zones A and B is greater than the spacing .theta.L which results from adjusting the detection zones to the farthest point L.

Abstract: An infrared detector device comprising a light projector adapted to output double-modulated infrared pulse light by modulating the amplitude of high frequency modulated light by means of low frequency waves, and a light receiver adapted to receive the double-modulated infrared pulse light. The light projector (1) comprises a 1/N-frequency dividing circuit (12) for dividing by N the frequency of the basic frequency signal from a basic frequency oscillator in such a manner that it can be set for switching, a second frequency dividing circuit (13) for dividing the frequency of the 1/N frequency-divided signal by a given factor to produce a low frequency signal, a frequency combining circuit (14) for combining the 1/N frequency-divided signal and the signal frequency-divided by a given factor, and a switch (17) for switching the frequency dividing factor for the 1/N-frequency dividing circuit (12).

Abstract: The disclosure relates to a crime-preventing infrared sensor of a passive type in which the infrared detecting element 6 detects the energy of infrared rays radiated from an object in a predetermined visual field to be monitored and an alarm is given in response to a detection signal outputted from the infrared detecting element. The crime-preventing infrared sensor comprises an infrared detector 7 for detecting a human body or any other object approaching the sensor itself independently of an object-detecting function in a visual field, whereby the obstruction in the visual field of the object-detecting function is prevented.

Abstract: A double eye type crime preventing sensor system comprising a pair of detection axes (6) substantially horizontally spaced apart and extending in substantially the same direction in a predetermined space, another pair of detection axes (7) substantially horizontally spaced apart and extending above or below the first pair of detection axes in the corresponding direction, a radiant energy focusing element (4) disposed at the terminal ends of these two pairs of detection axes for focusing radiant energy which comes in along the respective axes, two pairs of radiant energy sensing elements (8) and (9) disposed in the image forming position corresponding to the two pairs of detection axes in the vicinity of the focal point of the focusing element, the two elements (8a), (8b) or (9a), (9b), which constitute each pair of sensing elements (8) and (9) being connected in such a manner as to produce a substantially resultant sensing output when they detect energy in a time differential fashion, and a signal processing

Abstract: An optical system for an intruder detector which employs an infrared ray detecting element and a parabolic mirror above the infrared detecting element for collecting infrared rays from a detection region and directing them onto the infrared ray detecting element, and which has a detecting range through a wide visual field of 360.degree.. Reflecting mirrors 3 having the visual field of 360.degree. are disposed around the outside of a parabolic mirror and confront the parabolic mirror 1 around the outer periphery of the infrared ray detecting element 2. A window 5 which transmits infrared rays and does not shield the visual field of the mirror 3 mounts the parabolic mirror 1 at a prescribed position with respect to a base 6. A convex lens 15 located at the conical axis of the parabolic mirror 1 forms another detection region directly under the intruder detecting device. The intruder detector using this optical system is mainly for mounting on the ceiling of a house.