My belt is a "money belt" with a small concealed zipper compartment. I keep a spare car key in there.

For my house, I've installed a keypad lock on the garage door. So, in order to get inside you have to first key in a combination to open the overhead garage door. Then, enter a combination to open the man door to let you inside. As long as I remember the two combinations I don't have to worry as much about getting locked out.

I used to keep spare car and house keys in my wallet, but then I realized if someone ever mugged me, not only am I handing them my identification (with my home address on it), but I would also be giving them the means to get to my address before I do (the car key) and a way to enter the house unopposed (the house key). I figured that wasn't too smart.