A signal went off without a sound, prompting action toward an unseen threat. What could this be?

Category: Mystery · Difficulty: hard

Hint: Consider a type of alert that operates quietly.

Answer

A silent alarm

Explanation

A silent alarm can alert authorities without alerting the intruder, allowing for discreet enforcement.

This is a hard mystery riddle — a tricky one that takes a little thought. The answer is A silent alarm.

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