Once plugged in, the light comes on so you can stop in the darkest spot and it glows. It doesn't turn off. It can measure your tire pressure in real-time, and you can set it to automatic so it stops pumping air once it reaches your desired pressure. It's very handy to have a ball valve and two more I think for an air mattress and such. Not that noisy and doesn't move when placed on the ground, street or whatever.