Handcuffs with double locks have a piece that can stop the cuff from getting tighter. Tightening could be done on purpose or by struggling. Handcuffs may cause nerve damage or loss of circulation if they are tightened. Some wearers could tighten the cuffs to try to escape. They do this by trying to escape when the officer is loosening the cuffs. Double locks also make picking the locks more difficult.