Negative Positive
Title: Simple to install needs no battery.
Review: My house came wired with about 12 of these with the battery back-up. Since the 9 volt battery is supposed to power the entire system when electricity is lost they must be replaced fairly frequently. They test at about 8.25 volts when required to be replaced. I have purchased a couple of these non-battery units to replace the ones in the cathedral ceiling that requires a ladder to replace and will invariably start chirping at 2am on a cold winters morning. I have also replace the one in our unheated attic which suffers the same fate.As long as I can get to the unit I'll stick with the battery back-ups but for those hard to reach places these electric models as a better choice.
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