None of mine have collars, my Grans cat Sampson went missing for 3 weeks once, he eventually turned up but his front leg was broken & caught in the collar, he was terribly thin and very lucky to be alive. He had obviously got his collar caught on something, had broken his leg by trying to get free by putting it through the collar. So it has really put me off I'm afraid. Mine are chipped, but some people think a cat maybe a stray as they have no collar on, which worries me.