bought 3 packs of 2 at Costco November 2016. One never worked, I returned it to Costco. Now have 5. 1 year later, one kept going off without ability to stop it. Tossed it at city hazardous recycle site. Now 1 year later, the same with a second one. 3 of 6 left now. Will dispose of them also. They lie in advertising 10 yr battery life. They STOLE our money, and God forbid we ever need them to work if a situation arises, will never trust this company again! I no longer have receipts, A waste of time to deal with First Alert staff who could give a *** about anybody else! Do not make the same mistake everyone else has. This is your life, your family's life & your pet's life is at stake! Too bad we cannot sue the bastards!