The general alert siren goes off when there is a possible threat to the population.

Then the red alert sirens warbled and warning lights flashed.

All around her the lights were blinking red, alert sirens screeching.

At his words, yellow alert sirens began to whoop across the bridge.

D'Amelio's parting words echoed in his mind like an alert siren.

Not a red alert siren, but a wake-up call.

Someone had sounded the special alert siren activated only during station emergencies.

Julian's answer never came; the sound of the alert sirens cut off any reply before it had the opportunity to form.

The sound of the alert sirens was clear through the hatch.

"There," said Dax, as the sound of the alert siren reached them.