Smoke detectors are designed for the singular task of providing an early warning against potentially lethal concentrations of smoke or fire. Both the sensor and the alarm inside the smoke detector require electricity to function. To address this need, there are smoke detectors that function using the electric lines ("hard wired") in a house and detectors that rely on battery power only. Knowing the difference between hard-wired and battery-powered smoke detectors can enable you to choose the type that is more suitable for your living environment.
Limited Battery Life
The alarm inside the battery-powered smoke detector will eventually run out of power and cease sounding, unlike that of a hard-wired detector. If no one is home and you live in an apartment with thick walls, the neighbors may not hear the alarm during the amount of time that it is sounding.
Interconnected Smoke Detectors
Hard-wired smoke detectors can be interconnected -- which is to say wired from one to another -- so that they share the signal being received by the sensor on one of the detectors. Unlike a battery-powered smoke detector, this enables the hard-wired smoke detector that is sounding an alarm to activate the alarms on all of the other detectors it is connected to.
Hard-wired smoke detectors feature a battery backup that functions in the case of a power failure in the home's electric line. No secondary or additional backup for a battery-operated smoke detector exists if its battery should go dead.
The hard-wired smoke detector requires a disassembly from the wall or ceiling and disconnection of wiring if there is a problem, as opposed to a battery-powered detector which can be snapped open to remove the battery and replace it with a new one. This feature makes maintenance on a battery-powered smoke detector easier than if it is hard wired to the electric line.