This question already has an answer here:
Recently asked on Physics.SE:
RF engineers know that putting a big conductive thing like a human head near an antenna is going to significantly alter the radiated fields. The argument goes that putting the remote under your chin (or sometimes on your forehead, and sometimes with mouth partially open) not only arbitrarily alters, but improves the remote's effectiveness.
The "experiments" confirming this argument are typically something like this:
I tried unlocking my car, but it didn't work. Then, I put the remote under my chin, and it worked! Therefore, remote-under-chin is more effective.
This is a textbook case of selection bias. No one ever tries unlocking their car with the remote under their chin, and when that doesn't work, tries unlocking it normally.
Let's skip the speculation and discussion about how it might work. Can someone with access to some proper RF test equipment perform a well-designed test of a car remote's characteristics with and without human-head-in-proximity? Or, can someone cite similar studies already performed by qualified RF engineers?