Why not just have a deadbolt?
I read a tip in one of the topics that said to just have deadbolts on your rental houses and just buy regular knobs without locks. This will keep your tenant from locking their keys inside and calling you at odd hours. The deadbolt I have on my rental is the kind with the keypad instead of using a key. When I have to change tenants I can easily delete the old tenants code and put in a new one.
I thought this was a great idea and just wanted others opinion why this would not be a good idea or why you are not using this method. Before I saw that post I was going to contact landlordlocks and get some of those, but I dont think I am going to now.