In an electric bell-style alarm clock, the bell is rung by an electromagnetic circuit and armature that turns the circuit on and off repeatedly.ĭigital alarm clocks can make other noises.

In some models, the back encasement of the clock itself acts as the bell. Traditional mechanical alarm clocks have one or two bells that ring by means of a mainspring that powers a gear to propel a hammer back and forth between the two bells or between the interior sides of a single bell. Alarm clocks are also found on mobile phones and watches. A classic analog alarm clock has an extra hand or inset dial that is used to specify the time at which to activate the alarm. To stop the sound or light, a button or handle on the clock is pressed most clocks automatically stop the alarm if left unattended long enough. Some have sensors to identify when a person is in a light stage of sleep, in order to avoid waking someone who is deeply asleep, which causes tiredness, even if the person has had adequate sleep. Most use sound some use light or vibration. The primary function of these clocks is to awaken people from their night's sleep or short naps they are sometimes used for other reminders as well. An alarm clock (or sometimes just an alarm) is a clock that is designed to alert an individual or group of individuals at specified time.

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