A smoke alarm is a device that detects smoke, typically as an indicator of fire. Smoke alarms are usually powered by batteries or by mains electricity, and they sound an alarm when they detect smoke. Smoke alarms are an important safety device, and they can help to save lives by warning people of a fire so that they can evacuate the building.
Smoke alarms should be installed in every home, and they should be tested regularly to make sure that they are working properly. If a smoke alarm sounds, it is important to evacuate the building immediately and call the fire department.