Code reuires that line owered smoke detectors are on a circuit with a freuently used light.

This so you know its off, makes it impossible to just power off all the smoke detectors.

I am not impressed AT ALL, with those newer 10 year units.

First one I had the unit chirped and battery died at one year old.

My wife insisted on a long life 10 year smoke CO2 detector.

at 2 months old it failed, alarming for co2, she freaked and called the fire department, along came the police and EMTs