The fire dectector situation..... My dectectors are hooked up to the electricity in the house.... The only way a battery comes into play is when the house has lost power.... The battery is a warning system that lets you know 1 or both is draining. The battery will chirp when it's losing power, however there is a fail safe so that if both loses power it will be detonated for days. Removing the battEry only exacerbates the situation. Losing both will only make it mad.