I want to learn how to replace my old and probably non working electric smoke detectors. I can't afford the $150 the last electrician charged for changing over one I supplied. Somehow, that seems like an awful lot for less than 15 minutes work. I know he's skilled, etc. but cheesh ... I can't afford that sort of bill. I tried searching this site first for information, but couldn't find any. Sorry if I missed any threads about it, but "replace/ing smoke detector" only turned up suggestions to change the batteries twice a year. Clearly I have to flip the breaker off, but how do I locate which one a ceiling detector is on? Would it definitely be on the same circuit as the high hat near it? How can I be sure? Should I cut the whole house off to be certain? And, what problems might that cause? With the heating system and alarm system, etc. Thanks.