Simple Smoke Detector Repair - First Alert P1210 and Similar Photoelectric Models 

This is a simple and effective repair of a factory sealed smoke detector. Sealed models do not require any battery replacement. But the battery may die early. Sorry, I made a mistake in describing how a photoelectric smoke detector works. It is actually the opposite of what I described. When smoke enters the light chamber, the smoke helps make the LED light visible to the light sensor. If enough light, it trips the alarm.