If you have old smoke detectors, it is recommended that they be replaced every 10 years. My suggestion is to use one of these with a Lithium battery installed. This battery lasts for 10 years - the life of the detector. The smoke detectors + tax costs about $37.00 here at Home Depot. I am only charging $15 to install it.

ORDER 3 IF YOU WANT ME TO CHANGE ALL THREE IN THE UNIT.

**Be sure to put your unit number in the "Note" section at checkout.**