HomeKit and Heatmiser or Other smart stat

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Hi

I am trying to make my heating system smarter.

I have Heatmiser neo stats in every room with radiator controls and zone controls. Heatmiser works very well.

Now i want to control the stats when certain things happen.

  1. when no one is home - reduce any stat that is on to a lower temperature or maybe put them in holiday mode.
  2. for key rooms - using human presence detectors - turn the heating down if non one is in the room , and then put it back to the default settings if someone goes back into the room. I.e. in the lounge it may be set at 20deg in the evening, but if no one is in there change the temp to say 18 deg , but if someone enters again put the stat back to whatever the default in the stat is (in this case 20).

I am using the HomeKit integration , but i am not sure what homekit commands etc are valid.

Please can someone help?

many thanks