Abstract: The low battery level indicator is provided for a smoke detector. When the battery in the smoke detector becomes so weak that its voltage drops below a pre-determined value, an elongated, flexible signal member such as a tape or cord is released from the smoke detector so that it hangs down into the room below to persistently remind the occupant to replace the battery with a fresh one. The elongated signal member can be used together with a conventioanl device which emits audible periodic beeps or has a periodically flashing light to indicate the low battery condition. However, the long flexible signal member continues to hang down and remind the occupant that the battery must be replaced, even after the battery has gone completely dead and the horn and lamp no longer function. This invention constitutes a potential life-saving device.