Mice are very small creatures, and are good at disappearing into nooks and crannies. If you want to let your mouse run loose in your home for playtime, you’ll need to mouse-proof one of the rooms.
The safest room for a mouse is the bathroom. Close the toilet lid, plug up any holes or crevices, and remove electrical cords from reach. Make sure the entire floor is clean and chemical free. Keep the door closed to the room and make certain the bottom of the door is flush against the floor. A mouse can sneak through a gap as small as an inch, so if there is any room between the door and the floor, plug it up with towels.
If your mouse escapes and ends up loose in your home, confine any other pets so they don’t find your mouse before you do. Go to the hardware store and buy live traps that use bait. These traps are designed for the door to close when the mouse enters to get the bait. Place these traps all around the house with your mouse’s favorite food as bait. Check the traps several times a day. If you find a trap with a closed door, your mouse may be inside it. (Open the trap inside a mouse-proofed room or inside a different cage from the one your mouse lives in; it’s possible you have trapped a wild mouse instead of your small pet.)