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Why does a remote car key work when held to your head/body?

And also, similar claims abound.

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?


marked as duplicate by Joe Hass, Dave Tweed, Chetan Bhargava, Phil Frost, Matt Young Mar 6 '14 at 12:59

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  • \$\begingroup\$ I'm wondering if the answer to this will only ever be speculation until something really important is at stake - that's probably when someone will do the math or the experiment. \$\endgroup\$ – Andy aka Mar 5 '14 at 21:19
  • \$\begingroup\$ @Andyaka stackexchange reputation not important enough for you? :) \$\endgroup\$ – Phil Frost Mar 5 '14 at 21:20
  • \$\begingroup\$ Hee hee I'm not going to do a "well-designed test" and you asked to "skip" the speculation Phil!! \$\endgroup\$ – Andy aka Mar 5 '14 at 21:28
  • \$\begingroup\$ If I were to make a guess, I'd say that when the car fob doesn't seem to work it's because the E-field part of the transmission is somehow "bad" and H (on it's own) is \$\dfrac{1}{d^3}\$ - that's just the H-field and not the power relationship (going to be worse still). Putting it by a larger object improves the E side of the "EM" and you are back to transmitting power at \$\dfrac{1}{d^2}\$ \$\endgroup\$ – Andy aka Mar 5 '14 at 21:32
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    \$\begingroup\$ Duplicate of what? \$\endgroup\$ – JFA Mar 9 '14 at 20:47