The alarm clock is a type of clocks that are designed to show the time. But its main function is to awake people from sleeping or as a reminder of the time. There are different types and different technologies applied in the manufacturing of the alarm clock. The traditional alarm clock has a hammer-like small device and makes the sound of ringing bells. Some of them have advanced technologies like sensors to recognize a person's state of sleep. All smartphones come with alarms.
Some alarm clocks have radio receivers that can be used to awaken the person by automatically turning it on.
The alarm clock symbol in typing indicates the important dates in the text.