The safe is in the closet. You use something with a magnetic strip to lock it. When you come in it's open. You put something in, close it, swipe the magnetic strip and the light changes from green to red and it's locked. When you want to open it, you swipe the SAME magnetic strip and it goes red to green and opens.
Note that it's the magnetic strip that's the "key", not the keycode on the door. So say you use your KTTW card to lock it, your DHs KTTW card WON'T unlock it. Some people use their ATM card just so they don't forget which KTTW card was used!
In size, it's about 10 inches wide, 4-5 inches high, and maybe 6 inches deep on the inside.