I was very dismayed to find yesterday the temp change caused my magnetic lock armature plate to not seat properly, and a simple 4 lb pushed it open. Had to readjust custom made zl bracket.
Anyhooo... i soldered a wire to plate, planned to use continuity check. Problem is plate is almost always in contact... ie | or |/ .. therefore THAT idea is toast. so i figure i cpuld use leds and photodiodes across the plate. Id use pulsed signals to avoid ambient noise. If plates join, very little light is admitted thru..