silent alarm
noun
an alarm that alerts security personnel or the police without the knowledge of the intruder or criminal whose presence triggers it: The silent alarm set off a flashing light at the police station.
any visual rather than audible alarm.
Nearby words
silenced, silencer, silene, silenos, silent, silent alarm, silent area, silent auction, silent barter, silent butler, silent cop
Dictionary.com Unabridged
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019