One of the things that most FPS gamers are used to are bullet counters that tell you how much ammo is left in your digital weapon. I reckon that is an important bit of info to know in the real world too if you are in some sort of firefight.
If real bullets were coming my way, I would be too busy screaming like a little girl to count my shots. I would need something like this sweet bullet counter. It attaches to a weapon and counts the bullets as they are fired.
It is able to count the bullets using an integrated microcontroller and an accelerometer. The accelerometer registers a single bullet when it recognizes recoil in excess of 22.5g. It has time out so rounds fired aren’t messed up by vibrations after the shot. It’s apparently accurate enough that it could count automatic fire better than the people shooting and filming could.