Control device

PIR Motion Sensor

Sees changes in infrared, not movement — it detects a warm body crossing its beams.

Real part — tap a marker

PIR Motion Sensor

Sees changes in infrared, not movement — it detects a warm body crossing its beams.

Terminals

L — permanent live in
N — neutral (most mains sensors need one)
L' or SL — switched live out to the load
Some designs add a permanent-live loop or an override input

Fresnel lens — splits the view into beams
Pyroelectric element — generates a voltage when IR flux changes
Amplifier and comparator — decides what counts as a detection
Time (TIME) and light level (LUX) adjustment dials
Adjustable swivel bracket
Cable gland and terminal block

Cutaway of a PIR motion sensor showing the Fresnel lens, pyroelectric element, amplifier board, adjustment trimmers and cable gland

Cutaway — tap a marker

⚡ Meet it in a circuit

17Motion-Activated FloodlightAdvanced

Terms used here

Defined in the glossary — each one opens at its own entry.

⚠ Safety note

A PIR switches live, so the lamp holder stays live even with the sensor off — isolate at the board, not at the sensor. Detection zones are wider than people expect: a sensor pointed at a road or a neighbour's garden will trigger on passing cars, and one mounted near a heat source such as a boiler flue will false-trigger in still air.

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