I can see an easy way to detect you're in the dryer -- the temperature -- though that could be too late. Is there a cheap substance that makes a loud noise if you heat it up? I could see perhaps a little capsule of some alcohol that boils at dryer temperature, bursts and then vents out a whistle hole. But it would have to be pretty loud to hear it.

Perhaps better if you can figure a way to have something in the pen that a sensor in the dryer can detect, as that sensor can be much more expensive and the thing in the pens cheap. I don't want unique serial number RFIDs in my pens, though. Though there has been talk of RFIDs in clothes that contain the information on how to wash and dry them. In that situation, the dryer tells you you've put in a delicate item and should not have the heat so high, or perhaps put it in the dryer at all. Such a system could also work on pens -- and perhaps on fragile items that should not go in dryers, like cell phones and wallets.