The BébéSounds Movement Sensor will give you the peace of mind you won't get from just a sound monitor or even a video monitor. This monitor is an excellent value and it has 2 monitors in 1 so you don't have to purchase a sound monitor. The Angelcare Movement Sensor with Sound Monitor can only be used to monitor one baby at a time. If you have twins you will need to purchase two complete units. Please remember that the babies will have to sleep in separate cribs for these monitors to work properly. You will not be able to use Angelcare for more than two babies at a time because the monitor only has two channels. The Movement Sensor with Sound Monitor includes an under-the-mattress Sensor Pad, a Nursery Unit, a Parents' Unit (sound monitor) and two AC adapters. It can also operate with 8 AAA batteries (not included).