# Why do car keys have longer range when held next to your head?

I first saw this on Top Gear, and assumed it was a load of rubbish, but today I tried it out and it actually works, if you walk away from the car continuously unlocking/locking it until it stops, and go a bit further away so that the car will not un/lock. Then out the car keys next to your head and point them directly at the car it will un/lock.

How does your head/brain/etc increase the range of the keys? And why does it only work next to your head if you point the keys directly at the car, when you do not have to point towards the car when in normal range?

-
Probably has more to do with the height at which you hold the keys rather than their proximity to your head. – dbrane Feb 20 '11 at 13:33
@dbrane, I thought of this too when I was doing and so held it up at the height my head was and ducked. But afterwards I can see no reason why the height would affect it, both had clear lines of sight. As I understand it range should be a spherical bubble, so increase the height vertically on a spot outside of this "bubble" should increase the distance from the car, making the car further out of range – Jonathan. Feb 20 '11 at 13:45
This explains it Brain Increase in Car Key Range Of course, in this context "certified" may have other meanings. – Gordon Feb 20 '11 at 17:09
@Gordon: ??? what does that have to with the question, I'm asking physically, not psychically – Jonathan. Feb 20 '11 at 17:14
@Jonathan---obviously a joke. I am finding that this site needs to take itself less seriously. – Gordon Feb 20 '11 at 17:16

It works with a lot of body parts. It will work with a piece of wire too. This keys work at about 433 Mhz, a resonant Lamda/4 antenna is about 18 cm. Obviously the whole key is shorter, the antanna is not tuned for maximum power transmission. By bringing the key close to some conductive material, the power transmitted increases.

-
I have taken one of these apart before. The antenna was a copper trace running in a spiral around the outside of the PCB. I think it would be foolish if the engineers didn't design the antenna correctly, so that is probably fine. Also, I am very confused about the "pointing the key" comments people are making. I don't think it emits a roughly focussed 'beam' in any direction. So while I don't doubt people are seeing increased range, some of the details seem quite sketchy and anecdotal instead of systematic tests. – Edward Apr 9 '11 at 23:39
A similar effect can also be observed if you have a cheap AM radio with a random wire antenna, or a low-quality TV antenna (before the switch to digital signals). By moving your body (a large conductor) closer and further away from the antenna (staying within about half meter or so), you can easily affect the reception quality. – Willie Wong Apr 10 '11 at 0:33
@Willie, try the link in my answer :=) – Georg Apr 10 '11 at 10:15
FM reception increases considerably when the antennae is help in hands.. – Vineet Menon Nov 1 '11 at 14:53

It actually does increase the range. Here is the 'experiment' I performed once.

Walk away from the car and find the range at which the key fails to work. Walk away another 5 feet. Turn and put the key against your chest, so that it points towards the car through your body. It worked!! I did some more testing. Apparently the range increases by about ten feet if the key is used through the body.

I have no idea why.

-

## protected by mbqSep 22 '13 at 0:27

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).