What's inside a 1980s Racal-Guardall RLC1S PIR motion sensor. No instructions or details but most likely a 12 volt device which connected to a dedicated lighting control unit. Uses a segmented mirror to focus IR from the environment onto the sensor.

Also a look inside a modern self contained 230V AC PIR motion sensor which uses the same chip and very similar circuit. Uses a plastic IR lens to achieve the same results as the mirror.

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