49 MHz is the most common frequency used, but some also use 900MHz, while many digital monitors use 2.4 GHz, and DECT digital monitors use 1.9 GHz. It’s important to check the specifications on the model you buy. Older Wi-Fi baby monitors use a frequency of 2.4 Ghz, and newer Wi-Fi baby monitors use a frequency of 5.0 Ghz.