Welp, there is a lot of discussion around these claims.
But we are also on Telegram, mostly because I'm using their API for our Home-Assistant instance to deliver status updates (left the bathroom window open for too long, weather-forecast on the morning and evening for the next 3 days). I like it.
I'm using a ready-made sensor for this. It's the same system I'm using for temperature and humidty measurement. It's proprietary [0], but someone reverse engineered it [1], so I can send the data via MQTT to home-assistent. I then wrote an automation using Node-RED. It get's triggered when the window opens. After an initial timeout of five minutes, it will compare the inside temperature and humidity with the outside temperature and humidty, and decide if it should wait another five minutes or fire off a notification. If you close the window before, it will stop everything and reset itself.
[0]: https://mobile-alerts.eu/ [1]: https://github.com/sarnau/MMMMobileAlerts
Kind of odd that I trust Durov more than Zuckerberg, but here we are.