Bought this as a replacement for one that my husband managed to lose after one day! The idea is great but you have to untwist it when not in use so that the light turns off. I made the mistake of leaving it on my dogs collar then my husband took the dog out during the day and the light unit came lose and fell off. But with the new one we now unclip it after her evening walk and have managed to keep it for a couple of weeks now. It is extremely bright and as my dog is black it makes her visible on dark nights. Definitely recommend it for the price.