You have a few different options:
-
DIY: You can put a Raspberry pi with a display, speaker, camera, and a button at your gate and program it to send notifications when the button is pressed. You will have to get a good waterproof case for it too. Recommend doing this only if you know what you are doing
-
Pre-built: You can get a HA-supported video doorbell and you get all the requirements already built-in. I use the Dahua VTO-2202 and it has been working quite well so far. You will have to block it’s internet access and point it to an internal SIP server for the calling functionality to work. See a review here: The one 🔔doorbell🔔 to do it all! - YouTube
Hope this helps, and all the best!