One who or that which alerts.

comparative form of alert: more alert

Very attentive, or vigilant

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

plural of alerter

on guard

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

(US, Canada) A public notification of a child abduction.

A warning that indicates an emergency situation. / A state of readiness to deal with such emergency situation.

plural of amber alert