Abstract: Embodiments of a passive infrared detector can distinguish between an intruder and a small animal passing nearby the detector with a high degree of accuracy without substantially detracting from the ability to detect the intruder within a coverage area farther from the detector. In some embodiments, the passive infrared detector includes a pair of lens assemblies that collect infrared light onto corresponding infrared sensors. Each lens assembly receives light from different spatial regions, which do not overlap near the detector and which substantially overlap farther from the detector. The passive infrared detector also includes a controller that is capable of distinguishing between an intruder and a small animal based on simultaneity of signals from the infrared sensors or by summing the signals from the infrared sensors.

Abstract: A passive infrared detector that enables the extent of the field to be 360 degrees in circumference with a simple arrangement and allows the field range in the vertical direction to be adjusted wholly or partially. A plurality of sensor units are circumferentially arranged on a sensor mounting plate. Each sensor unit has a reflecting mirror and a sensing element placed at the focus position of the mirror. Each sensor unit is rotatable in the vertical direction. A slot is formed radially in the sensor mounting plate opposite to each sensor unit. A rotating plate is rotatably mounted on the sensor mounting plate. A circumferential slit is formed circumferentially in the rotating plate such that the distance from the center of the rotating plate to the circumferential slit gradually decreases. An adjusting rod is connected at one end thereof to each sensor unit. The other end of the adjusting rod extends through the slot and the circumferential slit.

Abstract: The present invention aims to avoid mutual interference of outputs of passive infrared detectors in an amplifier circuit of an infrared sensor to be amplified by a single system of amplifier circuit by cyclically switching outputs from a plurality of passive infrared detectors at a predetermined cycle. P.sub.1 and P.sub.2 each represents a passive infrared detector, and switches 2.sub.1 and 2.sub.2 can be switched over cyclically. Between an operational amplifier 12 and an operational amplifier 13, series circuits of capacitors and switches are provided in parallel as many as the passive infrared detectors. Switches 20.sub.1 and 20.sub.2 are opened and closed in synchronization with the switches 2.sub.1 and 2.sub.2 respectively. The capacitor C.sub.30 is used when an output from the passive infrared detector P.sub.1 is amplified, and a capacitor C.sub.31 is used when an output from the passive infrared detector P.sub.2 is amplified.

Abstract: A level of received light detected by a light-receiving means (R) is given to both an indication controller (11) and a transmitter (13). The indication controller (11) obtains a flashing frequency corresponding to the given received light level, and flashes an LED (12) at the frequency obtained. The received light level transmitted from a transmitter (13) is demodulated and decoded in a receiver (4) and then given to an indication controller (3). The indication controller (3) obtains a flashing frequency corresponding to the given received light level, and flashes an LED (2) at the frequency obtained. Thus, the operator can recognize the received light level readily and reliably.