We have an old dryer. One of those clunky models with a circular dial instead of a new-fangled digital panel of some sort.
The dryer no longer turns off when the timer runs out.
Regardless of what's in the dryer, I always use the Timed Dry setting and set the timer for 30-40 minutes. At the end of the cycle it will buzz quietly for a few minutes and then go on to the next setting. After air drying the contents for thirty minutes, it buzzes - again, quietly - and then moves on to the next cycle.
It will do this for hours and hours. Like if you leave the house and head to the zoo on a Saturday.... when you return three hours later the dryer will still be on.
And this is why I've posted a note-to-self on the main exit door.
The only way to stop this cycle of madness is to open the dryer. So before you leave the house, ask yourself, "Is the dryer on?"