@tanza:
I think the more important thing is to have them ID chipped. I don't keep collars on mine at home, so if they were to get out, they would have have collars with ID's… but they are chipped (before chips, tattoos)...
I had to sign an agreement with Medfly to always keep Buddy's collar on with ID tags. You see he slipped out last Oct, was chipped but I did not have his collar on. Karen at Medfly was none too happy. In the past I never had my last 2 wear their collars in the house either and never had any problem because if they got out they never left the front of the house.