Very attentive, or vigilant

on guard

(programming) Capable of receiving and responding to notifications from other threads of execution.

An alarm. / A notification of higher importance than an advisory. / (military) A state of readiness for potential combat.

To give warning to.

A community in the Qikiqtaaluk Region, Nunavut, Canada; the northernmost permanently inhabited place in the world.

awake and ready to notice danger or problems

One who or that which alerts.

comparative form of alert: more alert

The quality of being alert or on the alert