Photoelectric: This type of detector responds to a reduction in light reaching an internal photocell. When smoke goes into the unit, the light is scattered and the alarm sounds. These detectors respond more quickly to smoldering fires than ionization smoke detectors. In addition, because these detectors are less likely to send out a false alarm, they are less likely to be a nuisance. However, this type of smoke detector will not alert you when the batteries are dead.
Whichever smoke detector you decide to use, both should have their batteries changed annually. We recommend picking a day every year that you will remember, like New Year’s Day or your birthday, and go around the house to test your detectors and change the batteries.
There are also many manufactures of smoke detectors and each different one may have a test button that is not the same as another. There are no design standards here and some old models don’t even have test buttons, but a lever or other device to test the smoke detector.