Alarm clock

An alarm clock is a clock that is designed to make an alarm sound at a specific time. The primary use of these clocks is to awaken people from their sleep in order to start their days in the mornings, but they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock needs to be pressed, and some stop automatically after a few minutes if left unattended. A classical analog alarm clock has an extra "hand" that is used to specify the time at which to activate the alarm.

Traditional mechanical alarm clocks have a bell on top that rings, but digital alarm clocks can make other noises. Simple battery-powered alarm clocks make a beeping sound whereas novelty alarm clocks can speak, laugh, or sing. Some alarm clocks have radios that start playing at specified times, and are known as clock radios.

In a mechanical bell-style alarm clock, a spring drives a gear that propels a clacker back and forth between two bells or between the sides inside a single bell. In an electric bell-style alarm clock, the bell rings with an electromagnetic circuit and armature that turns the circuit on and off again repeatedly.

Clock radios

Modern digital alarm clocks typically feature a radio alarm function as well as a beeping or buzzing alarm, allowing a sleeper to awaken to music or news radio rather than harsh noise. Most also offer a "snooze button", a large button on the top that stops the alarm and sets it to ring again at a short time later, typically anywhere between five and 10 minutes. Some alarm clocks also have a "sleep" button, which turns the radio on for a set amount of time (usually around one hour). This is useful for people who like to fall asleep with the radio on.

Newer digital clock radios often use a battery backup to maintain the time in the event of a power outage. Without this feature, digital clocks will reset themselves incorrectly when power is restored, causing them to fail to trigger the alarm.

Computer alarms

Alarm clock software 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. Some examples are Alarm Clock Pro and Citrus Alarm Clock; both which sport numerous enhancements above the standard bedside alarm clock.

While PCs allow features and flexibility ideal for office reminders, some people still prefer the simplicity and bedside convenience that an ordinary alarm clock offers for morning waking.

In recent years, more and more people have programmed the computer to automatically play from a playlist of songs every morning to wake them up. This is done by using the "Task Manager" in their Control Panels to activate the playlist at a set time every day. Since these playlists are often the users' most favorite songs, they have something to look forward to waking up to every morning.

Next-generation alarms

Among annoyances caused by alarm clocks is sleep inertia, a feeling of grogginess that results from abrupt awakening. Progressive alarm clocks claim to solve this issue. They include sunrise alarm clocks, dawn simulators and progressive auditory alarm clocks.

Scientific studies on sleep having shown that sleep stage at awakening is an important factor in amplifying sleep inertia, alarm clocks involving sleep stage monitoring have also appeared on the market in 2005. Using sensing technologies such as EEG electrodes (SleepSmart from Axon Labs) or accelerometers (SleepTracker from Innovative Sleep Solutions and aXbo), these alarm clocks are supposed to wake people only from light sleep.

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Clock radios

Computer alarms

Next-generation alarms

See also