We stopped using ours when DD went into her big bed (a king single) at 26 months. She was in a toddler bed from around 20 months but as she was (and still is) quite the terror and VERY adventurous (I found her in her GroBag on top of the change table one afternoon ), we used the movement monitor to know when she'd gotten out of bed. I would hear just the first warning beep and wake to turn it off - and then hunt down DD!