Given that my other car got broken into today (2 windows smashed, and car gutted from the inside out) my biased advice would be to not leave your key hanging around under the frame...

As for your trunk locking - yes it is possible and I experimented with that when I first got my NAH. If you have the key wrapped in layers of clothes that you just throw in the trunk, the fob will not always be picked up by the car. I know it's strange because (last I checked) radio signals are not supposed to be obstructed by clothing, but I have run into this same scenario :-)