Anyone breaking it by entering the grounds triggered a warning buzzer.

There is the sound of a warning buzzer, very loud in Sarah's ears.

A red light flashed on the control panel, and a warning buzzer sounded.

It sounded its warning buzzer, and Paul stepped out of its path.

I could tell from her expression I had added another amber light and a warning buzzer.

The warning buzzer fell silent and the blinking red light went off.

She pushed the door to the room aside before it had a chance to open completely, ignoring the warning buzzer.

The warning buzzer sounded, then the bell for round one.

All of his internal warning buzzers were going off.

The warning buzzer sounded as I took the keys out of the ignition.