These detectors were installed in our new home in CA and used about 14 months when the home inspector improperly told the relocation company they had to have 30 year batteries installed that could not be tampered with. These all have the door opening for a 9 volt battery backup and are to be wired into your primary power. Asking $50 for all 6 smoke detectors and 3 smoke and carbon monoxide detectors as a package.