Colbyt wrote:
Many models are compatible so you may not need to buy all new but if
they are more than 5 years old I would buy all new with battery
back-up.

Thanks. Do 120-volt smoke detectors with battery backup just have a a
battery in each one? If so, and the power goes off, does that just change
all of the smoke detectors to individual detectors with no interconnectivity
feature?