I use HomeKit to control a few smart devcies at home, is tado° compatible?
It is, as long as you have a V3 Bridge (known as an Internet Bridge).
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Actually Frank you forgot the annoying fact that the Tado AC product still does not support HomeKit - not even the v2 model. 😥
Even more annoyingly there are no other equivalent products available with HomeKit support for AC. The leading competitor Sensibo's Smart WiFi AC also lacks HomeKit as does every other one. This category of product uses an IR transmitter to send remote control signals to a standard - typically dumb Air Conditioning unit.
It could be the original reason for none of these supporting HomeKit was due to Apple originally not supporting IR devices however Apple did add support for this about a year ago although zero so far IR based products have yet become HomeKit approved.
With global warming I would imagine a lot more interest in AC products even in supposedly temperate Northern Europe and the UK whereas Mediterranean countries would I expect already commonly purchase AC units.
There are technical reasons why the V1 and V2 Smart AC Control cannot be made HomeKit compatible. We thought we could get it HomeKit compatible and in theory it is possible but our WiFi Chip does not support IPv6 only IPv4. The issue is that HomeKit requires that the device fully supports IPv6. This was not clear in the design phase. This issue makes it impossible for us to make the Smart AC Control HomeKit compatible.