This diagram shows an infrared movement detection system that uses a pyroelectric sensor behind a Fresnel lens to detect movement in a given area. An infrared source sends out waves that reflect off objects and return to a receiver as echoes, allowing the system to sense distance through transmitted and reflected waves. The sensor then outputs a signal when it detects infrared waves from the source that have been reflected off moving objects in the detection area.

3. Pyroelectric
sensor
Fresnel lens
Detecting area
Infrared source movement Output

4. Distance
Reflected wave (echo)
Receiver
Transmitter
Original wave
Object