One of the new things in "Halo: Reach" is armor abilities which include sprinting, jet packs, invisibility, and armor lock.
When you use armor lock, it freezes up your spartan armor making you invisible. This is great if you are about to be splattered or hit with a rocket. However it leaves you crazy vulnerable and it's really easy to kill someone as soon as they come out of an armor lock.
![](https://i.ytimg.com/vi/I-4DmFnGeOU/mqdefault.jpg)