Transformers: War for Cybertron

This achievement is relatively easy.

The second Decepticon mission has plenty of Cloakers in it. Play as Starscream since he has a sniper-type weapon, Null Ray I believe it is called. After you finish the section with the Autobot floating platform that is projecting a shield over a doorway, you'll come across your first Cloaker. Follow him into a room that will have several in it. You'll be able to tell where a Cloaker is by his charging Plasma Cannon. Hold the Left Trigger button to go into sniping mode. Find one that is charging his Plasma and aim just a little bit higher and to the right of it (if you are head-to-head) and pop a shot off.

I was able to do this on Hard and it basically one-shotted the Cloaker.

I spent forever trying to guess where their head was at and snipe it. I failed each time. Then with one of the Machine guns I ran straight at a cloaked one just firing my gun off and once he died my achievement popped. So over time you will get this achievement just spray and pray these guys and hope you peg'em in the head.

Try Escalation when going for this because they swarm there.

Just to clarify: if you play like I do, you will probably get this eventually on the campaign. (When I play, there's more led in the air than in Chuck Norris' diet or in a Chinese paint can.)

However, if you do not earn this in the campaign, a very easy location is in chapter IV, checkpoint 'Across the bridge'. Choose easy difficulty and character Breakdown. Proceed for about 15 seconds and you will encounter approximately 10 cloakers. Make sure you have your Scatter blaster equipped and start scatter blasting! Try to aim at head height. If you run out of ammo, there's more on the hallway. If you run out of cloakers, just press start and restart from the last checkpoint.

Don't spend time trying to pinpoint these guys with a sniper rifle like null ray.

Just equip a shotgun-like spread weapon like Scatter rifle/gun/ray whatever it's called. I got this achievement on the second cloaker I ever encountered in campaign just by aiming high-ish with a shotgun.

Like stated in the other solutions, I found the shotgun to be very effective in headshotting these little buggers.

The easiest way to target these guys when they're cloaked, is while they're charging their shots. For a little over a second before they fire, their gun tips glow... just aim a bit over the glow and you'll get the achievement.