This article has multiple issues. Please help improve it or discuss these issues on the talk page . A bicycle lock is a security device used to deter bicycle theft, generally by fastening the bicycle to a fixed object, e.g., a bike rack.
The only line of defense against bike thieves is a bike lock. If you're going to actively use your bicycle and leave it on the streets, you have to lock it properly. If you lock it, but not the right way, it will get stolen.