Detecting Voltage/Signal Changes on NodeMCU

I have a challenge with detecting voltage/signal changes.

I have an Aiphone intercom that is connected to a video door station. The only signal the Aiphone puts out is a video signal when the door station button is pressed i.e. when someone rings the door bell, the video feed starts.

The video feed is the only signal output available to tell me that someone is at the front door. I really want to use ESPHome to detect the video signal and then send an alert to me.

Here’s the page from the Aiphone manual.

Screenshot from 2021-06-17 20-43-22

The BR (brown) and RD (red) wires are the ones I am focusing on as they provide the video feed when the door station is activated. I am wondering if the video feed would be possible to monitor? The voltage is very low when there is no video, and then the voltage rises when the video starts.

Would be interested if anyone has done such a project previously?

All the ESP boards have an ADC.

Which you can then use to trigger a template binary sensor:

Sounds like exactly what I need. Thank you for the feedback, will give it a go.