The alarm clock is a specific clock, designed to awaken a person at a predetermined time. The main function of an alarm clock is to awaken people from sleep, as well as short naps, and can also be utilized as a reminder device. While many alarm clocks utilize sound as a means to achieve disruption, others can use lights. Other—newer—alarm clocks can be rigged to roll around the room, or even fly above the sleeper’s body, in order to make the sleeper engage physical activity that will awaken them. Other, newer, alarm clocks use sensors to determine a person’s sleep schedule, and will avoid waking them during a deeper sleep cycle. By awakening an individual during a light sleep stage, they will wake up more refreshed, and less groggy.

An alarm clock uses a standard dial, or buttons, to set the targeted time, and will emit the according stimulus to awaken the user. To stop the sound, users must press either a button or handle. Many clocks will cease emitting noise and light if left unattended for long periods of time, and many clocks include a “snooze” function, which allows users to wake up gradually to intermittent alarms. Many traditional alarm clocks have several bells, that ring through a mainspring. The mainspring propels a gear that knocks a hammer back and forth between these bells, creating a ring. Other alarm clocks utilize electric noises preloaded into a digital circuit.

Alarm clocks appear in various shapes and designs, and utilize different methods to awaken the user. While some use a piercing sound, to shock the user out of sleep, others feature calming sounds—like running water, or bird noises. Many modern alarm clocks make use of clock radios, and some include iPod adapters. While many adaptations of the alarm clock exist, their function remains constant. Alarm clocks have served sleepers for many years, ensuring they awaken at a predetermined time.