This is the Jablotron Nanny Monitor which monitors breathing and movements. It will inform you if the babies breathing falls below a dangerous threshold. It is a certified medical device and is used in maternity wards in some European hospitals. The sensor is 30cm x 30cm so has a large surface area and it just lies on a flat surface under the mattress so not suitable for a slatted bed or cot. It is easy to use and is powered by 2 x AA batteries and the battery level is checked when it is switched on. There is the choice of buying the sensor with one or two sensor mats depending on the size of your baby and how much they fidget.