Alarm Remote Amplification via head?

June 2, 2006 6:37 PM

A long while ago I picked up a tip that you can extend the range of your car alarm remote by pointing it at your head. I've been trying this for a couple of years and it seems to work, but obviously I have my doubts. Is there any rationale behind this?

I specifically put the remote right under my chin. I've tried the remote from long distances, couldn't get it to work. Place the remote under chin, it works. The more I think about it the dumber it sounds. What do you think?

posted by puke & cry to Grab Bag (11 answers total)

Your body is acting as an antenna.
posted by nathan_teske at 7:02 PM on June 2, 2006

Currents are also induced in tissue (as well as any other conducting or dielectric materials) upon exposure to electromagnetic fields. Although hands and bodies are not particularly efficient radiators, they will scatter a fraction of the power incident on them, depending on the RF frequency involved. Back at the receiver, the scattered signal will compete with the original signal from the transmitter, combining either constructively or destructively depending on the relative distances to the two signal sources. At the same time, the proximity of the scatterer to the antenna can influence how efficiently it transfers power to the receiver. Thus reception can be either improved or degraded, depending on the placement of one's body.
posted by porpoise at 7:08 PM on June 2, 2006

Despite being a scientist, and despite having a father who is an expert in how these types of things work, I don't have a good answer for you (although I like porpoise's answer).

That said, I do the same thing, and I truly believe it works.
posted by nekton at 7:59 PM on June 2, 2006

It seems highly unlikely to me that this actually makes any difference.
posted by Steven C. Den Beste at 8:06 PM on June 2, 2006

I have noticed that this does seem to make a difference, but a little experimentation seemed to indicate that the difference was due to the fact I was holding the transmitter higher than I would normally hold it. This means it's less blocked by the bodies of other cars, etc.
posted by tomble at 8:25 PM on June 2, 2006

Best answer: According to the editors of New Scientist, the chin thing works thanks to capacative coupling.
posted by mendel at 9:01 PM on June 2, 2006

Best answer: To add to mendel's answer, you are made of mostly water. More then that it is salt water. If I recall correctly, salt water is much more conductive than fresh water. There is a high frequency signal to get through your non-conductive (insulation) outer shell into your highly conductive inner core through that capacitive coupling mentioned in mendel's link. If you want to know more about this a quick run through of high-pass and low-pass RC networks at wikipedia may help (or maybe not, depending on your background).

You are a large antenna. Note how well the reception gets while you adjust the bunny ears on your television, but as you step away the picture gets crappier and crappier. Does anyone have bunny-ear antennas for their TV anymore. I sure do....

You are also organic. This means that you have a lot of electrical conducting lengths. The length of a conductor plays a big roll in how an antenna works. How well an antenna works for a given frequency (or wavelength, rather) is related to its physical lengths.

In the case of your remote, placing the device on your chin might be a good combination of a lot of different lengths. A couple of which may radiate very nicely to the receiver in your car at the frequency that your antenna system is operating at. So that may help explain why your chin has better gain then any other parts of your body.
posted by nickerbocker at 10:03 PM on June 2, 2006

Mod note: a few comments removed
posted by jessamyn (staff) at 12:54 AM on June 3, 2006

Check out the answers to The Amazing Radio Man. It occurs to me that under the chin maximizes capacitive coupling because it maximizes the amount of body surface area while minimizing distance.

I think you need to try sticking it under your armpit to see how well it works from there. If the effect is anything more than imaginary, your armpit should be even better. You might have to get right in at the skin though, eww :P. I wonder if this trick works for people with beards.
posted by Chuckles at 6:51 AM on June 3, 2006

ISTR Click and Clack discussing this in depth, so there may be info at the Car Talk site.
posted by rlk at 10:50 AM on June 3, 2006

It makes me wonder why the remotes aren't designed to take advantage of this. Heck, most people have their alarm remotes on their keychains -- why not use some kind of wire mesh strap to hold it onto the ring and use the whole keychain as an antenna?
posted by kindall at 4:04 PM on June 3, 2006