An alarm is something used to alert people quickly to something. Most alarms use loud noises and/or flashing lights. Some alarms may use other ways of attracting peoples attention quickly, such as turning off loud machinery, shaking a bed or pillow.
Types of alarms
Alarm clock - A clock designed to make noise to wake up people. Burglar alarm - An alarm that sounds if a person tries to enter a building without permission. Siren on an emergency vehicle (ambulance, fire truck, police car). Severe weather sirens - Used to warn of severe weather, such as tornadoes or tsunamis. Klaxon - A type of siren, known for it's distinct sound. Often found on submarines. Fire alarm - An alarm for warning of fire inside of a building.