Rush inside where I have replacement batteries, try to figure out how to open the key but totally fail. In my spare stuff drawer in the kitchen find my spare key, and take both keys with me. The main key also has a ring with all my house keys. Yes, I do mostly use the keypad on the carport door, but Murphy says if I don't take my door keys along, when I get home the keypad battery will have died.
One of the first things I did when I got my laptop out at the hotel was watch the video on how to replace the battery. It is not intuitive. There is some irony here - embedded in the key assembly is a small dagger-like object which can be used to open the door if the battery in the key is dead. However, you can't start the car once inside without a live battery. This gadget is removed by sliding a switch and pulling. Once that is removed, it can be used to pry open the case, and from there replacing the battery is standard.
When I got back home, one of the first things I did was replace the battery.