The app records every change and where it came from. Changes I make on my phone say app. Changes made by the schedule say schedule. Eleven of them say device, which means somebody pressed the buttons.
I have a smart thermostat. Ordinary, popular brand, the round one, on the wall in the hall where the old one was.
The history is the whole of this so I will be exact.
Every temperature change is an event, and every event has a source. There are four sources and I have checked them all against my own behaviour over three years.
`schedule` means the programme did it. Mine goes on at six and off at eight thirty, on at four and off at ten.
`app` means I did it on my phone, and the event carries which account, and there is one account, which is mine.
`auto` means one of the clever features, geofencing or the eco setting, and I have those switched off.
`device` means somebody turned the dial and pressed it on the wall.
Since 2022 there are eleven `device` events.
They are all between 02:20 and 03:05.
They are all the same size: the target goes from wherever it is up to twenty four degrees, which is the highest my dial goes to before it needs a long press, and which nobody in this country actually wants their hall to be.
And they all end about forty minutes later with another `device` event putting it back to exactly the number it was before.
Two of the eleven happened while I was in Cornwall.
I know that with the certainty of a receipt. It was the last week of August, I was in a rented cottage with my sister and her family, four hundred and some miles from my house, and I have the fuel receipts and the cottage booking and about nine hundred photographs.
The thermostat history has a `device` event at 02:41 on the Tuesday and another at 03:19 putting it back, and one on the Thursday at 02:33 and back at 03:11.
The other nine are all nights I was asleep upstairs.
What I have checked, and some of it cost money.
Whether `device` can be produced any other way. This is the important one, so I went at it properly. I rang the manufacturer's support, twice, and the second person I got was clearly technical and stayed on the line for half an hour with me.
Her answer: `device` is written when the physical input on the unit is used. Not the app, not the API, not a voice assistant, not the schedule. Those all have their own source values, and she listed them, and none of them can appear as `device`.
She also confirmed that the history is written server side from what the thermostat reports, and that the thermostat reports the source itself.
Whether somebody was in my house. The doors were locked and my neighbour has a key and was in Spain for one of the two Cornwall nights, and I would trust her with my life anyway.
Whether the unit is faulty. It was replaced in 2023, under warranty, after I sent them the history and made a nuisance of myself. The new one has done it four times.
The forty minutes.
I have added it up because it is the only thing about this that has a number attached to a real world effect.
Forty minutes at twenty four degrees in a hall at three in the morning in a house that is otherwise off costs about ninety pence in gas, and my boiler fires, and the pipes tick, and that is a thing I have heard.
The first time I heard it I thought the boiler was faulty and I got a man out, and he found nothing and charged me eighty five pounds and told me my system was in good order for its age, which it is.
The bills carry it. Eleven nights of a forty minute burn across three years is not visible on a bill and I only know it is there because the smart meter's half hourly data has it and because the thermostat's own energy report attributes it.
The one thing I did that I would not do again.
In the January I set an alarm for two in the morning and I sat on the stairs in the dark with a blanket, because the pattern is 02:20 to 03:05 and I wanted to see the dial.
You can see the thermostat from the fourth step. It has a little ring that lights up orange when it is calling for heat and it is the only light in the hall.
At about twenty to three the ring came on.
I did not see anybody. I want to be completely clear about that, because the story would be better if I said I did and I am not going to.
What I saw was the ring come on, and the display change from the small standby number to the big one it shows when you are adjusting it, and then step up, the way it does when you turn the dial, in the little increments, one at a time, about a second apart, from seventeen to twenty four.
And then the press. The display flashes when you push the whole face in to confirm, and it flashed.
I was eleven feet away on the stairs looking straight at it.
I have taken it off the wall.
The heating is on a plain programmer in the airing cupboard now, the kind with the little tabs you push, and the hall has a blanking plate on it, and it cost me two hundred and forty pounds to have a man come and change it back.
The account still exists, because I could not bring myself to close it, and the history is still in it, and there have been no events of any kind since the unit came off the wall in the February.
What I cannot stop doing, and it is the reason I have written this down, is checking. Once a week or so, on my phone, in bed. There is nothing there. There has been nothing there for eight months.
But the app still shows the device as connected, with a battery level, and last week the battery level went from ninety four per cent to ninety three.
It is in a box in the loft with no wires on it.