early warning system

1. A network of sensing devices, such as satellites or radar, for detecting an enemy attack in time to take defensive or counteroffensive measures.
2. A system or procedure designed to warn of a potential or an impending problem.

A specific procedure for the early detection of any departure from normal frequencies of clinical cases or serological reactors of specific diseases by monitoring a sample of the population at risk.

The noun has one meaning:

Meaning #1: a network of radar installations designed to detect enemy missiles or aircraft while there is still time to intercept them