An alarm clock is a clock that is designed to make an alarm sound at a specific time. The primary use of these clocks are to awaken people from sleep in order to start their days, but they can also be used for other reminders. To stop the sound, a button or handle on the clock needs to be pressed, or it stops by itself after a few minutes. An alarm clock has an extra "hand" that is used to specify the time to "go off".

Traditionally, alarm clocks have a bell on top and which rings, but newer alarm clocks can make other noises. Simple battery powered alarm clocks make a beeping sound while novelty alarm clocks can speak, laugh or sing. Some alarm clocks have radios which start playing at a specified times.

Recently, alarm clock programs have been developed for personal computers. A PC acting as an alarm clock may allow an unlimited number of alarm times, personalized tones, online features (such as news and weather reports), and even features for insomniacs. While PCs allow features and flexibility, however, most still prefer the simplicity that an ordinary alarm clock offers.

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