Your body can become part of the antenna
A car key fob sends a brief radio signal from a very small antenna. At the frequencies commonly used by remote keys, that antenna is much shorter than the radio wave it sends, so its shape and surroundings can strongly affect how efficiently it radiates.
When you hold the fob against your chin, your body can couple to the antenna: radio-frequency energy moves between the fob and your body, which can behave like an extension of the antenna. The body may also change the direction in which the signal radiates. If more of that energy travels toward the car, the receiver may detect the signal from farther away.
Why it works only sometimes
This is not your chin boosting the signal like a powered amplifier. The fob still transmits at the same power; the way its signal is launched and distributed changes. The result depends on the fob’s antenna design, how you hold it, your position relative to the car, and obstacles or interference along the path. In some situations, your body can absorb or redirect energy the wrong way instead.
So the trick is a small antenna effect, not a special property of the car or a reliable range upgrade. It is most likely to help when the fob is just beyond the receiver’s ordinary reach—and a slight change in how the signal spreads is enough to get it through.
