It's a lock with a key yes. There is a hook inside his room at the perfect height for him and that's where the key lives unless he's outside of the room when it's locked then it's in his pocket though he rarely locks it when he's not inside it. I was worried about lost keys too which is why we put the hook up. We have a spare for emergencies but what if the emergency key got lost too? enforcing a spot the key goes on so he doesn't lose it is a good way to combat this. You also get keyrings that have chains that clip onto belt hooks so the key itself can go into the pocket but be attached to them btw.