oh, that is a very good question, i was wondering the same thing. i put bells on 3 different places, the ones placed at the doors, she didnt react too, however, the ones i placed upstairs on the rail, she played with constantly. so then i took those down, and removed the other bells from the second door, and put all 3 bells in one spot, which is mostly the door she goes out of, and now i'm seeing more improvement with her sometimes ringing the bells, or simply just sitting at the door!! Good luck. =)