Your car key fob broadcasts the signal in all directions. Your skull behaves like a satelite dish and reflects the radio signal all in one direction. It's a bit like a TV satelite dish that you have on your house wall - but in reverse.

RF can be mysterious. Any answer here is probably correct.

If, like on Star trek, we had  Geordie's visor to put on, we could see the RF leaving the key fob and at which edge it is strongest.

If... we could also see the RF waves, and the reflected waves from the ground, and from you, heading to the car, arriving in phase or out of phase, then all would be clear.

Look here:

http://www.youtube.com/watch?v=Sm3_qEMTdc4

Imagine You had to do such acrobatics to activate

Your car lock!.

Georg

The black magic of antennae design (until supercomputers came along)

4 possibilities:

chwaral answered one.

the radio signal (100s mHz) pass through glass much better than steel, Try it with the remote at head height but to the side of your head.

these frequencies with the antennae designs used are fairly directional (45 degrees - see diagram in link below.) Try it at head height but face the remote 90 degrees away.

the capacitance of your head may cause the antenna to "draw more power" from the electronics. This could be proved by measuring the current drawn from the battery. The output power design is regulated by the authorities but this measurement is done assuming "normal" use.

http://en.wikipedia.org/wiki/Remote_keyless_system

The TV program in question is purely entertainment orientated and its content should not be taken at face value.

Having said this, it is true that antenna height above ground is strongly related to the range of VHF/UHF radio systems.