What Tado sensor can I use for when it is set manually to heating?

So I am new to HA and want to make my first automation.
I can find the Tado sensors like temperature and humidity and I understand how they can be used in a automation.
I want my automation (to turn on a smart plug) when the Tado radiator thermostat is put in heating mode either manually of digital.
I dont want to set it on a fixed temperature, because that would trigger it when it is hot weather.
But I dont know where to find the correct sensor/trigger input.