Holding the fob to your head (or other dense, boney structures) actually is an amplifier for the fob to send the signal. Your skull works very well as a radar dish to bounce the signals off of, and strengthen the signal. That being said, no idea what it does to the 'soft' bits inside the skull. I would never expect everyone to take my word for it, so please look it up......amazing what you can learn from a few searches! I asked the same question, and found a whole physiology clinical on the topic. I use that trick rather frequently.

