Old thread, but i second hiding a key outside. I've seen some pretty creative ideas on where to hide the key (google for some great ideas!).
Honestly, if I hadn't hid the key outside, I probably would have been locked out like 5-6 times in the last year. I'm used to having a keypad on my garage door, and leaving the door from the garage unlocked. I don't have the keypad anymore, so leaving without a key (exercise, going outside in general) usually lands me locked out!