Is there large demand for this? I just cook when I'm home and ensure to turn the oven off when I'm done. I'm sure there are people out there who appreciate the automation, but a) how many and b) how much would they pay for it?

Ask not how much customers are willing to pay for it, ask instead how much data collection companies are willing to pay for customer data.

C) it only makes sense if your habits are completely predictable, like cooking food 15 minutes after leaving work or something.

Why? Just carry a dongle and when that is not in the vicinity of the house switch of certain circuits. What do you need the internet for?

> Just carry a dongle

The problem is nobody wants to carry a dongle. Also, localizing the dongle inside the house is not as straightforward. Would the users need to put one dongle-detector in each room? one near each exit? If it has long transmission range, then it would probably be big/heavy due to larger batteries.

Why a dongle? Lets just embed a chip into everyone at birth.