Iirc, the "stealthmeter" indicates how detectable you are, not if you have actually been detected...
You should try to play without in GWX, there are plenty of ways to know if you have been detected. Warships will obviously start coming your way and probably shoot at you, merchants will start zig-zags and if armed will also start shooting at you.
At night, expect searchlights and starshells to indicate clearly you've been detected...
