I have been looking for a system that allows for HDMI text overlay (without the need for an additional PC (XMBC) etc), from Indigo to my TV for some time, and came across the following....
https://www.inair.tv/
The website pitch mentions "Future updates will offer a notification system to offer alerts for whatever you want."
The plan would be to integrate Indigo, so as notifications / CCTV images could be sent via WiFi to my HDMI TV (whilst I was watching), and overlayed on the screen. The system does look a 'little Big Brother' with it's content inspection, however it's one of the cheapest systems I have seen to break into the cryptic world of HDMI
Vangelis