My kitchen has glass cooktop stove. Suggestions on hi ow to detect if it's left on? One problem with just placing a temp sensor nearby is that even after turning it off, the surface remains hot for some time.
What I want to accomplish: if stove is on, and no motion in kitchen for maybe 10 minutes, then alert somebody.
Never used it and not directly compatible with Hubitat, but its marketing says it will do what you want...
If I remember right, @danabw had a neat setup using some contact sensors.
I do, but my approach is dependent on the cooktop design/knob layout...my guess is that modern stove designs (my cooktop is from 2004) aren't going to work w/my approach using hidden contact sensors. But the deets are here, and part of larger topic on monitoring cooktops/stoves w/lots of ideas.
OH MY GOD LOOK AT ALL THE WHITE COOK MARKS!!!
Sorry - could not resist. 100% cleaner than my cooktop, believe me. 
Yeah, you're either going to need to find some way to monitor power use by the stove, or heat (which has the issues of carry-over as you mentioned). Tougher nut to crack.
Read through the topic I pointed you at, there are ideas there that do not involve knobs or contact sensors.
Use a power monitor. Iotawatt unfortunately is not available any more but there are
still few other high power sensors. Aeotec is one.
We no longer have a glass top stove, but when we did we found that Weiman's Glass Stovetop cleaner worked wonders on marks like that. Start with a razor blade to get off the worst and then apply/buff apply/buff the Weimans and it will look like new. Gentle, almost flat scrapes of the new razor blade is the way.
You should use an HEM and clamp to the the circuit (the stove is on it's own circuit) and monitor activation of power draw and turn off of power draw to trigger your notification rule.
In case you aren't familiar, by HEM @rlithgow1 is referring to this:
https://www.amazon.com/Aeotec-Aeon-Labs-ZW095-ZW095/dp/B00XD8WZX6/ref=sr_1_4?
Usually something you'd have an electrician install, unless your very comfortable poking around in your circuit panel.
Search Amazon for "current switch" - depending on your wiring, one of the clamp types might allow you to install it without opening your breaker box.
(Of course, these kinds of sensors merely close a dry-contact switch when current is detected; you'll need some other device to get that signal into your Hub. I used a spare Konnected input with mine.)
I wish I had this before my husband burnt the bottom my favorite Dutch oven to our new glass oven stove top 
Wouldn't monitoring just power draw not be effective? It seems like you would want something for each cooking element, not just the overall appliance. if you are cooking multiple things, the overall power draw won't help you much to know when your eggs are done my the potatoes are not. Maybe I'm just overthinking it.
I think the goal as stated in the OP is to detect when someone has finished cooking and left the kitchen but forgot to turn off the (electric) stove.
Not sure what use case you have in mind.
That's why you go gas or induction.
Thankfully our new house has a propane stove and I love it 
But, would have been nice to be able to leave the old stove when we sold this house.
Depend. Each burner has very somewhat unique power draw pattern. With fine tuned thresholds
you might be able to tell which exact burner is on. But frankly, I absolutely see a use case for
this. From the other side, detecting the stove is on is very useful. Recently friend of mine
left something cooking and left an apartment. Gladly he thought about this potential disaster,
rushed to home and came back just a right time. Next day he asked me if it is possible to check
remotely if stove is still on and if yes, to turned off. My answer was "yes". In a next few days my
induction stove was equipped with the ability to check status and remote on/off control.
few RM rules immediately was created to prevent a potential disaster. Guess what? His case
inspired me to automate my stove but his one is still is not automated.
I have an induction. So what? It is still possible to create a disaster
(specifically with gas fired).
My core requirement is:
Think of it like Tesla 
... If no hands on steering.. get attention of the user.
Any current/power sensor is needed to detect "stove on (any burner)" condition.
This is a job for motion/presence sensor.
I also added DIY on/off switch (63A NC Contactor + ZWave Relay).
And of course, few rm rules for warnings and auto off.
Download the Hubitat app
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