I haven't tried this yet, but I'm guessing you could lock the FOB in the trunk. Consider this scenario:

1) FOB in your shirt pocket, no other FOBS inside the car. You park your car, get out, close the door and lock the car via the button on the door handle

2) You walk over to the trunk, open it, bend over to retrieve something -- now the FOB accidentally slips out of your shirt pocket and into the trunk without you knowing..

3) you close the trunk and go on about your business..

Now.. will the TCH warn you that the FOB is inside the car/trunk? Will it allow the trunk to be closed? Will it unlock the doors when you close the trunk with the FOB in it?

I just thought about this scenario. I may give it a try later tonight.