Detect if outdoor gas grill is left on?

I would like to detect if the outdoor gas grill is left running too long. What’s a good way to do this? I was thinking of using a temperature sensor inside the grill cabinet, below the grill itself. It probably gets up to about 125 degrees or so down there when the grill is on (guessing, I have to try it). But the extra SmartThings motion detection device I have laying around that I’d like to use for this says the operating temperature only goes up to 104 degrees F… Ideas? Thanks.

You could add a valve and valve control. Wound not actually determine if it was on, but sure would ensure it was off. Heck you could even use it to automatically shut off after x minutes.