This document discusses pyroelectric sensors and their use in detecting human movement. It contains the following key points:
1. Pyroelectric sensors can detect rapid temperature changes caused by human movement, but are sensitive to air currents which can trigger false alarms.
2. The sensor works by detecting the infrared radiation emitted from warm bodies using a lens to focus the radiation onto two sensing elements. As a heat source moves, it exposes one element then the other.
3. For outdoor use, the sensor requires protection from rain and wind. Focusing lenses and shadow masks are used to improve detection range and create a detectable signal pattern from moving heat sources.