It is a tire PSI tester, that you leave on your valve stem. It is color coded so at a glance you can tell if your tires PSI is too low/too much/just right. I don't check my PSI as much as I should, this is perfect for the laziness in all of us! It uses a hex nut at the bottom of it to secure it, and prevent theft. I don't know how well this will work out in the end, but they've already met their goal and still have 39 days to go, I'm thinking about backing it to get a set of 4 to test out. Doesn't really make sense to have these on a new car since TPMS already does this, but our older cars it's perfect.
EDIT: I also forgot to put, that on their kickstarter they are saying that you can fill up your tire without taking this off of the valve stem.