We bought pack of two at Costco. Few days later one went off in the middle of the night. No sign of smoke anywhere. Scared us half to death. Two days later the other one went off in middle of the night! Again no smoke! I called First Alert. They sent me two new detectors - free. Same model. Guess what. Last night the new one went off at 4am. No smoke!!! This is ridiculous- recall this product. Id give it zero rating if I could