How Does an Alarm Clock Work?

Do alarm clocks turn off after a while? Learn how long an alarm clock goes off and how long the alarm on the iPhone goes off.

Updated: October 5, 2022

Alarm clocks, as annoying as they may sometimes be, are quite interesting pieces of technology. If you've ever wondered how an alarm clock works, here is an explanation.

Analog Alarm Clocks

Analog alarm clocks feature a round numbered clockface with separate hands for hours, minutes, and seconds. The clockface sits on small legs, usually on the bedside table. On top of the clock are two bells with a hammer between them that goes back and forth when it's time to wake up.

The clock mechanism

Inside an analog clock is a set of gears that move the hands of the clock around. Traditionally, analog clocks called wind-up alarm clocks were powered by being wound up. Inside the mechanism was a spring which, when it was wound up, slowly released itself to power the gears. Attached to the gear mechanism was an escapement wheel and an oscillator. These kept the time accurate by regulating the speed of movement of the gears.

Nowadays, many analog clocks are powered by electricity and work like digital clocks.

The alarm

On the front of an analog clock, there is a hand that is different from the other hands of the clock. Often smaller and a different color, this hand is there to set the time for the alarm.

Within the analog clock is a mechanism that causes the hammer to rattle between the bells. When the alarm is not in use, a spring prevents this mechanism from activating. However, when the alarm is switched on, the spring is released when the clock's hour hand reaches the position of the alarm hand. This allows the alarm mechanism to activate and rattles the hammer between the bells.

Digital Alarm Clocks

While some people may be familiar with the fact that analog clocks have gears that turn the hands and keep time, fewer people are familiar with how digital clocks work.

The clock mechanism

Digital clocks usually use a quartz crystal oscillator to keep time. This is normally powered by either mains electricity, a battery, or kinetic energy. This oscillator sends a regular fast repeating signal to a receiver within the clock's circuitry. After the clock receives this signal, it is converted to a new signal of exactly one hertz (one signal per second). This signal of one hertz is then used to drive the clock's timekeeping mechanism.

As the clock receives the correct number of signals to pass either a second, minute or hour, signals are sent to an electronic chip that converts the time into a display on the clock's screen.

The alarm

When you set an alarm on a digital clock, a signal is sent to activate the alarm when the correct time is reached. Often the alarm sounds like either a recorded alarm sound or a radio station. Some modern digital alarms wake people up with light in order to replicate the days before alarm clocks. Other alternative alarms are available as well.

Online Alarm Clocks

Online alarm clocks are the latest addition to the world of alarm clocks, and many people wonder if they are different.

With an alarm clock online, your browser's time acts as the trigger for the alarm. When the alarm time is reached, the alarm clock's software picks this up and sounds the alarm that has been set.

Author: Burak Özdemir

My name is Burak, and I used to have difficulties waking up in the morning due to unreliable alarm clocks. Over the past few years, I've dedicated part of my life to finding the best alarm clocks and sharing my knowledge with people through this blog.