Have just bought my 10 year old some of these. They screw onto the valve instead of the cap and light up when the bike moves. Have a feeling he may think they're not very cool and I will have wasted my money. They looked better in the packet than on the bike. I like to think anything that helps being seen on the way to school is a good thing. We'll see. They don't fit DS1's bike as he has presta vavles so he escapes which means I have a spare set that could go on mine 