
I use a bulb camera from Amazon for my doorway, because it is very easy to set it up since just goes into the existing bulb socket without any additional wiring, and connects over wifi to my internet. Most of these cameras are based around V380 / V380 Pro platforms, which are typically nice to work with 3rd party software via the ONVIF and RTSP protocols. ONVIF allows good control over the camera besides just streaming, and RTSP allows you to only stream the camera feed to other devices, such as your phone or tablet. But basically the end result is that you can use great software like Synology Surveillance Station to monitor the camera and control it remotely, which is what I do. Or you could also use things like VLC on your computer to just watch the feed. If you really want to play around with it, you can install scrypted on a server and connect the camera to almost anything like Apple HomeKit or Google Home.
