Alarm clock

The primary function of these clocks is to awaken people from their night's sleep or short naps; they can sometimes be used for other reminders as well.

Most modern televisions, computers, mobile phones and digital watches have alarm functions that automatically turn on or sound alerts at a specific time.

285–222 BCE) fitted his clepsydras with dial and pointer for indicating the time, and added elaborate "alarm systems, which could be made to drop pebbles on a gong, or blow trumpets (by forcing bell-jars down into water and taking the compressed air through a beating reed) at pre-set times" (Vitruv 11.11).

[3] The late Roman statesman Cassiodorus (c. 485–585) advocated in his rulebook for monastic life the water clock as a useful alarm for the "soldiers of Christ" (Cassiod.

[4] The Christian rhetorician Procopius described in detail prior to 529 a complex public striking clock in his home town Gaza which featured an hourly gong and figures moving mechanically day and night.

In 1235, an early monumental water-powered alarm clock that "announced the appointed hours of prayer and the time both by day and by night" was completed in the entrance hall of the Mustansiriya Madrasah in Baghdad.

[7] From the 14th century, some clock towers in Western Europe were also capable of chiming at a fixed time every day; the earliest of these was described by the Florentine writer Dante Alighieri in 1319.

In 1497, Simone Campanato moulded the great bell (h. 1,56 m., diameter m. 1,27), which was put on the top of the tower where it was alternatively beaten by the Due Mori (Two Moors), two bronze statues (h. 2,60) handling a hammer.

Workers were late for, or missed completely, their scheduled shifts in jobs critical to the war effort.

[18] The clock may turn on the radio at a designated time to wake the user, and usually includes a buzzer alarm.

A few popular models offer "nature sounds" like rain, forest, wind, sea, waterfall etc., in place of the buzzer.

In the event of a power interruption, older electronic digital models used to reset the time to midnight (00:00) and lose alarm settings.

Many newer clock radios feature a battery backup to maintain the time and alarm settings.

[21] Native applications, however, can wake the computer up from sleep using the built-in real-time clock alarm chip or even power it back on after it had been shut down.

[24] The alarm clocks use sensing technologies such as EEG electrodes and accelerometers to wake people from sleep.

Alarms which can connect to vibrating devices (small ones inserted into pillows, or larger ones placed under bedposts to shake the bed) also exist.