Aliens: Dark Descent

As you proceed through levels, you have a detection bar in the top right of the screen.
As your spotted by aliens, this will increase, starting at easy, through medium and finally to hard.
Between each section of the bar, you'll see a red "!" mark. When it reached this, you'll trigger a massive onslaught, a timer starts and then a number of aliens comes out of a spawn hole when it hits zero and they come straight for you. This number goes up as the planetary infestation level increases.
Back yourself into a corridor or a tight space and set up whatever turrets you have and you should wipe the onslaught out.

I'd say this is pretty much un-missable but I suppose if you played through the game perfectly you might be able to avoid triggering this. This was one of the first achievements I unlocked.