[triangleman83]

Have you ever taken them completely off the ceiling or just opened the battery cover? My house has 120v/9v detectors and when I was installing fire alarms in new construction, all residential multifamily and hotels had 120v smoke detectors in the units which are interconnected. They also have 9v batteries for backup. Marriott hotels actually specify 24v system smoke detectors tied into the main alarm system. I know Home Depot sells battery only detectors but those are generally for retrofit applications. A contractor will likely have to install 120v in anything new being built.

[smackfu]

Here's a very common battery-only smoke detector: http://www.homedepot.com/p/First-Alert-Battery-Operated-Phot...