smoke detectors do something similiar(at least Photoelectric smoke alarms do) when they first detect smoke(by the lightbeam being interupted/scatterd and thus the current changing on the sensor) they send out a couple more light flashes in quick sucession(they usualy send a beam every so often(i think it was every second or 5 seconds? anyway, not constantly)to check if the disturbance was just a dust particle or actual smoke THEN it rings the alarm....

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not hard to implement something similiar into this i imagine.