Purpose: To allow parents to monitor their babies activities remotely.
Issue: Many of the new monitors use DECT technology to transmit a signal. These monitors transmit a cellular signal continuously. This is not good for your child (or you). Even the 900MHz monitors are not good.
Better Option: Choose 900 MHz over DECT and a wired monitor if at all possible. These are the safest option. Do not use WiFi cameras and monitors (optimally keep WiFi turned off when your baby is sleeping). In a perfect world, you should be able to be close enough to your babay to monitor them directly.