alarm (clock) noun [C]
a clock that you can set to wake you up at a particular time with a loud noise:
I've set the alarm for 7.30.
The alarm went off at 7.30.
alarm clocks N-COUNT
An alarm clock is a clock that you can set to make a noise so that it wakes you up at a particular time. I set my alarm clock for 4.30. Syn:
alarm