Inside a heat detector alarm. (Not a smoke detector.)

Heat detectors are very useful where there's a risk of deliberate smoke or haze on a regular basis that would cause false triggering of a traditional smoke detector. The complicated units can sense a sudden increase in temperature associated with a fire, while simpler units just have a set temperature threshold.
This one has a very weird bit of circuitry that had me double checking the schematic. If you've got any ideas about it then leave a comment down below.

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