OK, here is one for the books ... Three hard-wired smoke detectors and a non-stop but intermittent chirping downstairs and upstairs. "Easy", you say, "Go to the Big Box store and ask them what to do." Four guys gathered around, accused the lady of being crazy, decided it was a big electrical problem and she should call an electrician because the circuit has a BIG problem. With chirping in the background, I get the call. Smiling, you look up from your book and say: "Easy, just pull the detectors and change the backup batteries." Intermittent chirping continues but not clearly from one place. "OK", you say, "You forgot to drain the capacitors." Done. Chirping continues. "OK, damnit", you say, "Kill the breaker to the detectors for 5 minutes then put the detectors back in." Done. Chirping continues. "GRRRR", you say, "Make sure the circuit is off, disable the communicator wires, re-install the new detectors, turn the power back on." Done. Intermittent chirping in your face! Give up yet?? Did you notice the lady had a separate plug-in carbon monoxide detector laying on the stairs which had been in use for over a year? Did you know that damn thing has battery backup? Pull the battery out of the CO2 detector and ... blessed silence. Who would have known?