Gas hob left on.

Surely the best solution is some kind of switch that puts a light on when the gas is turned on at all, as if its lit then you would know if a pan is on it, if its not and you did not smell it it could be dangerous too. I'm surprised this is not done already for safety. My electric oven has a light when the thermostat kicks in and a different one when its not, so to speak. It also has lights for the rings on the hob. Of course ironically in my case lights are a bit pointless! I can at least use my pocket light detector to tell if they are on or off though. Since the RNIB light detectorcan detect infra red, then I suppose one can use it to see invisible flames as well. Brian