A fire alarm is a device that detects smoke or heat and makes a loud warning sound to alert people that a building might be on fire. When a fire alarm goes off, everyone needs to leave the building immediately and gather at a safe meeting spot outside.

Most fire alarms have two parts working together: sensors that detect signs of fire, and speakers or bells that create the warning sound. The sound is intentionally loud and hard to ignore, often a repeating beep or a continuous ringing, because in a real fire, every second counts. Some fire alarms also include flashing lights to help people who are deaf or hard of hearing.

Buildings like schools, offices, and apartment complexes are required by law to have fire alarms. They're tested regularly (which is why you sometimes hear them go off during fire drills at school). While false alarms can be annoying, fire alarms save thousands of lives every year by giving people time to escape safely before smoke and flames spread.

The term can also refer to the broader fire alarm system that includes pull stations (red boxes you can activate if you see a fire), control panels, and connections to the fire department. When someone pulls the fire alarm, they're manually activating this system to warn everyone of danger.