VTech BM2220 Audio Monitor comes with safe and secure digital transmission, which prevents anyone other than you from listening in. Thanks to the room temperature sensor, the baby monitor lets you know if the nursery room is too hot or too cold for your little one. The baby unit operates on mains power OR rechargeable batteries, can play 5 lullabies with 5 level volume setting, and has a soothing glow on night light. With support for 2-way communication, it lets parents and babies talk with each other through the baby and parent units. It has low battery and out of range audible alerts. The parent unit and baby unit will operate on the included rechargeable batteries for when mains power is not available.