Easiest way to get this foolproof would be to put an induction loop around the power cable and use the reading from that as a proxy for on/off state.

It would catch any case where the stove is drawing power, irrespective of possible failure modes of the stove itself.

Is your market people with anxiety/OCD about whether they turned off stove?

Your idea would be a hard sell to anyone paranoid enough, since they won't trust your monitor.

An alternative would be to install a safety key switch or a magnetic safety key. The paranoid can then check they have the key on them when they leave the home (like the lady worried about her hair dryer - see below).

Or perhaps a camera facing the oven switch?

Scott Alexander wrote https://slatestarcodex.com/2014/11/21/the-categories-were-ma...

  The Hair Dryer Incident was probably the biggest dispute I’ve seen in the mental hospital where I work.

  Basically, this one obsessive compulsive woman would drive to work every morning and worry she had left the hair dryer on and it was going to burn down her house. So she’d drive back home to check that the hair dryer was off, then drive back to work, then worry that maybe she hadn’t really checked well enough, then drive back, and so on ten or twenty times a day.

  It’s a pretty typical case of obsessive-compulsive disorder, but it was really interfering with her life. She worked some high-powered job – I think a lawyer – and she was constantly late to everything because of this driving back and forth, to the point where her career was in a downspin and she thought she would have to quit and go on disability. She wasn’t able to go out with friends, she wasn’t even able to go to restaurants because she would keep fretting she left the hair dryer on at home and have to rush back. She’d seen countless psychiatrists, psychologists, and counselors, she’d done all sorts of therapy, she’d taken every medication in the book, and none of them had helped.

  So she came to my hospital and was seen by a colleague of mine, who told her “Hey, have you thought about just bringing the hair dryer with you?”

  And it worked.

  She would be driving to work in the morning, and she’d start worrying she’d left the hair dryer on and it was going to burn down her house, and so she’d look at the seat next to her, and there would be the hair dryer, right there. And she only had the one hair dryer, which was now accounted for. So she would let out a sigh of relief and keep driving to work.

  And approximately half the psychiatrists at my hospital thought this was absolutely scandalous, and This Is Not How One Treats Obsessive Compulsive Disorder, and what if it got out to the broader psychiatric community that instead of giving all of these high-tech medications and sophisticated therapies we were just telling people to put their hair dryers on the front seat of their car?

  But I think the guy deserved a medal. Here’s someone who was totally untreatable by the normal methods, with a debilitating condition, and a drop-dead simple intervention that nobody else had thought of gave her her life back.

monitor home's phases and just learn AI how to spot patterns to identify each device. I think there was a product doing that already..