Initial reasoning for call out was because the smoke detectors were making noise when there was no smoke present. After inspecting the units I found that they were installed when home was built in 2007. The units were manufactured 10/06. This is well past the recommended replacement time frame of 10 years. You could even smell plastic burning inside the old units. We replaced the old bedroom units (4) with new hard wired units with 10 year lithium ion back up batteries. These units do not need battery replacements for the entire life of the unit. We also install 3 new smoke/ carbon monoxide detectors in the home to meet safety and code requirements being that the home has an attached garage. These units were install in place of the top floor hallway unit, 1st floor hallway unit and the basement unit. Once installed we ran a test cycle on the units and they all checked out properly.