Unfortunately this is the only reliable way and later on even that doesn't work so you have to result to a lot of sneaking.

One thing that does work from time to time, thought it might be because of a bug, is to distract the group with either the Beret's decoy or the Spy, and then bring up the Seal behind them with the harpoon gun. Problem is that gun, while silent, takes a long time to reload and honestly this tactic only works about 50% of the time.

Now there are some levels where depending on distance, gun fire and even grenades won't set off an alarm but you really just need to experiment with that.

Thanks very much for the reply, very much appreciated!

What determines whether or not being spotted sets off the actual alarm that gets more soldiers piling out of the garrisons?

2 things:
1) if you've already blown up the garrison. Don't laugh. There are missions where this becomes a must.
2) Distance. Sometimes the opening dialogue will mention this but sometimes you have to play around with it. Someone up in a cliff isn't likely to hear gunfire down below and so on.

Ah ok, I've been trying to sneak all the time because I thought the big alarm always got set off with the sound of gunfire etc. but I'll play around with it more and see what I can get away with!

Thanks!

The real challenge of this game consists in getting through missions while avoiding this patrols. Otherwise it would be damn easy. Using the bug with the seal is pretty much cheating. You might as well put the invincibility code.

That said, there are missions where you just can't get away with winning the mission without raising the alarm.