It has a strong magnet and has never fallen off the holder. It also works in automatic mode, when it senses that it is dark enough, it turns on the lamp itself and turns it off when it is bright. I highly recommend it!

Light is great! Works as it should, lasts long, smart mode is literally "set it and forget it". It stay off during daylight, and starts automatically when it gets dark. There are 3 rubber attachments, so you can put it on any tube on your bike, even the thin ones (my seatpost is short, so i could not put it there)