The easiest Outpost to do this is the
Kyra Weigh Station Outpost. The Coordinates are X: 340.0 Y: 379.0. Here are only 1 Alarm and the Outpost Difficulty is easy.
The Alarm Button is on your Minimap displayed with the Loudspeaker Icon. Ingame you see a big Loudspeaker mast and below is a yellow Box, the Alarm. Here is a picture of it
Sneak to the Alarm, disable it with
and then kill all Enemies here, after you disable it does not matter whether you will be detected. If you have already liberate the Outpost, use Outpost Master to replay the Outpost.