I have a customer that has called saying her smokes are 2 years old since the last replacement.they work for about the 2 years and then they start going off consistently. The Home was built in 2001 . The smokes are hardwired and the brand is kidde.... There wasnt any problems during the 2 years until now. These are not battery back up. any ideas I am sure she will want to replace them again but She figures they should last more than 2 years. We are in a dry climate .She has turned off the circuit for the smokes and has 2 small children It is a higher end type home.