A staple of sci-fi prop design is slapping ammo counters onto guns. Because that’s what the future is like.

Jokes aside these are aftermarket grips that can be purchased to track the numbers of rounds in a magazine. They come with a special magnetic follower the end user is expected to install in their magazines to track the remaining ammunition.

They do not count the round in the chamber. Which could present safety concerns in inexperienced hands.

It seems the company, Radetec, who makes them also does so for a few other designs. Here’s a few: