A battery operated smoke detector with a system for lowering the battery of the smoke detector is disclosed. The smoke detector is of the type that is mountable from the ceiling of a structure. The battery of the smoke detector is part of a battery pack that is connected to a battery wire that is mounted on a spool. An engagement mechanism that allows the lowering of the spool and battery pack in response to a low-voltage condition controls the lowering of the battery pack. An electric motor is connected to the spool, and is used for raising the battery pack once a battery that is charged is connected to the system.