People shouldn't forget that old school (non-WLAN) baby monitors usually don't have any encryption, and can be easily intercepted.
WiFi baby monitors at least have WPA2 encryption over the stream, but firmware (and any cloud software if you are using such features) can be quite sketchy, if you are not using reputable brands (and even that is not a guarantee.)
https://www.youtube.com/watch?v=YWGFMFeg5zc