At first we thought this was a lighting detector (for photographers), but upon closer inspection we realized it was a lightNing detector. You know, the type that tells you if there's lightning. The thing has a convenient belt clilp and tells you whether lightning's 20-40 miles away, 12-24 miles away, 6-12 miles away, or less than 6 miles way.
We're not sure how well this works, but it's probably useful than relying on your own eyesight to tell you whether Storm's coming. Yes, we're talking about the X-Men character. She's very angry.