A more likely theory is that the fob transmitter (and antenna) is tuned to put out max signal when near the body. This is it's normal use.<p>If however you tested it with the fob somewhat isolated it would then be out of tune.<p>eg in the factory it would be tuned at a set distance from a "dummy body".<p>It's the same with a walkie-talkie radio. The antenna must be tuned when held in the hand, as your body provides the missing earth or ground-plane.<p>You can easily demonstrate this. Mount an antenna on a ground-plane with a length of coax, a SWR meter and a transmitter. Tune the antenna so the SWR is 1:1 and then move you hand close to the antenna. Once your hand gets withing a wavelength or so, the effect of the "detuning" can be readily seen on the SWR meter.
When I was a kid I had a tv where the quality of the picture noticeably improved when you touched the antenna... and I had recently heard that humans were mostly water... So I grabbed a glass of water and set it on top of the tv near the antenna and the picture cleared right up. Unfortunately this event made me the IT support guy for the family from then on...
The answer posted with all the experiments is conducted with a 2009 GTI, which reminds me of my first car, a Jetta from a generation before that. Its manual included this helpful illustration of the full expected range of the remote:<p><a href="https://imgur.com/a/1Pdfyg4" rel="nofollow">https://imgur.com/a/1Pdfyg4</a><p>Yes, apparently they were only willing to promise it would work within about arm's length of the car! It wasn't that bad, but also it wasn't a heck of a lot better, either!
When goofing off while tracing wires with a tone generator[0], we used to press the detector wand into our head, lick our finger tips, then run our fingers along the contacts on the 66 block[1] until we heard the warble from the tone generator.<p>0 - A troubleshooting and wire identification tool consisting of a battery-powered generator that produces a distinctive warbling sound and an inductive detector with a speaker that allows you to hear the warble when placed near the correct wire pair. Most look like this: <a href="https://www.grainger.com/product/EXTECH-Tone-and-Probe-Kit-40180-8EV89" rel="nofollow">https://www.grainger.com/product/EXTECH-Tone-and-Probe-Kit-4...</a><p>1 - a wiring terminal commonly used in the telephone system. <a href="https://en.wikipedia.org/wiki/66_block" rel="nofollow">https://en.wikipedia.org/wiki/66_block</a>
This effect 100% works, I’ve tried it many times over 20 years with many different cars.<p>It is best if you hold the flat side of the remote up against your chin.
Not sure I agree with the cavity theory. I suspect it’s you, you big ole bag of salt water, acting as a capacitive ground plane for the antenna. It’s like mounting a ham or CB antenna on a car and having the metal of the car not be in direct contact with the ground, but it acts as a capacitive ground plane. You can do something similar with a vertical antenna using ground radials in a star pattern on the ground.
Keysight Labs did some testing on this a few years ago. <a href="https://www.youtube.com/watch?v=AjYyjQKW-pU" rel="nofollow">https://www.youtube.com/watch?v=AjYyjQKW-pU</a>
I used to use this trick when I worked as a photographer of used cars. You'd get some 10-20 fobs and be expected to walk a lot of ~300+ cars and take images of them. Holding the fob up to your chin was the trick to finding the right vehicle... assuming the battery wasn't dead.<p>I still use this trick today to find my car when I park somewhere I am unfamiliar with.
Because I saw this headline, I tried to hold my key fob to my head today to lock my car, but it didn't work and I had to walk closer. So, there's one data point for you. Maybe I'm doing it wrong
It also works holding it near your torso, don't have to use your head.<p>Although, the joke you tell your friends is that it only works if they open their mouth and stick out their tongue like a satellite dish.<p>The fact that it works next to your torso made me think it was just a matter of bouncing half the radio emissions towards the vehicle, thus doubling the signal. Just like someone holding an omni-directional campaign lamp close to their body increases the light headed in a certain directions.
top gear (UK) demonstrating this in practice (potato video quality) <a href="https://www.youtube.com/watch?v=_jACSPipPSE" rel="nofollow">https://www.youtube.com/watch?v=_jACSPipPSE</a>
Sixty symbols (same author as Numberphile) video on this from 9 yeas ago: <a href="https://www.youtube.com/watch?v=0Uqf71muwWc" rel="nofollow">https://www.youtube.com/watch?v=0Uqf71muwWc</a>
Good explanation I found on YouTube few years back -
<a href="https://youtu.be/0Uqf71muwWc?si=eLDi_zvMtXJeh_WZ" rel="nofollow">https://youtu.be/0Uqf71muwWc?si=eLDi_zvMtXJeh_WZ</a>
It’s because the antennas in fobs lack an effective ground and are typically unbalanced. The body acts as an RC choke, creating a short on the ground side of the antenna (a typically intentional part of the design). The closer the fob is to your body mass, the better it will perform. Bone may also act as a reflector to some degree, and height can play a role.
I am disappointed to see no mention of "passive radiator" nor "parasitic element" on that page anywhere: <a href="https://en.wikipedia.org/wiki/Driven_and_parasitic_elements#Parasitic_elements" rel="nofollow">https://en.wikipedia.org/wiki/Driven_and_parasitic_elements#...</a>
Sixty Symbols did a video on this almost a decade ago: <a href="https://www.youtube.com/watch?v=0Uqf71muwWc" rel="nofollow">https://www.youtube.com/watch?v=0Uqf71muwWc</a>
Wow, I first heard about this in the early 90's in high school! I was told to hold it under your chin. It <i>seemed</i> to work, but I never formally did any experimentation nor did I have the statistics base back then. I still did it up until I got a proximity fob a few years ago. However, I always felt silly because I thought it was an old wives tail from my childhood. Very cool to learn there's actual science behind it.
Interesting!<p>>"This is a really interesting question. It turns out that your body is reasonably conductive (think salt water, more on that in the answer to this question), and that it can <i>couple to RF sources capacitively</i>."<p>Related: Capacative Coupling: <a href="https://en.wikipedia.org/wiki/Capacitive_coupling" rel="nofollow">https://en.wikipedia.org/wiki/Capacitive_coupling</a>
Used to have a radio transmitter that plugged into my car lighter, and hook up to an mp3 player (or whatever) and transmit that on a radio frequency that the car could pick up. Often it would be staticky unless I set the device on my leg, and then it got a lot clearer.<p>Always assumed it just kind of turned my body into an extra large antenna. Probably works for a key fob in a similar way.
This saved me from blistering cold just yesterday night. Car was too far for the webasto heater to receive signal from the fob. Tried multiple times, then remembered this trick. And yes, car picked up the signal when sent from the forehead.<p>Warm car in winter, yeah
Am I the only one for whom this doesn’t work? If I try to unlock the car with the fob against my head, my car doesn’t seem to receive any signal. But if I try and unlock the car from the same distance, key fob not on head, it works like normal.
<i>There were no large structures around accept for the concrete encased stainless steel vacuum tube of the LIGO Livingston Interferometer which runs parallel to the measurement axis and extends for kilometers in both directions.</i><p>amazing.
When TV still used analog broadcasting, and you were using a rabbit-ears antenna, and, if the signal was at all weak, you could walk around the antenna several feet away and see the effect on the TV screen.
I mean, it's electromagnetic waves. The right wavelength will bounce off things and increase likelihood of receiving a coherent signal. Works for a lot of things; RF, sound, light. RF has low energy and huge wavelengths. IIRC keyfobs are in the 200-600MHz range.<p>Ha, found some (kind of) evidence:<p>Radiowave Effects on Humans - March 28, 1980 / T. Neil Davis (<a href="https://www.gi.alaska.edu/alaska-science-forum/radiowave-effects-humans" rel="nofollow">https://www.gi.alaska.edu/alaska-science-forum/radiowave-eff...</a>)<p><pre><code> One reason the question is unanswered is that the energy absorbed by a human from radio waves depends upon the relationship between the size of the human and the frequency of the radio waves. Just as a TV antenna of the right length and orientation picks up the best signal (the most energy) from a transmitted wave, so it is with a human being. It appears that the cranial cavity of a mammal will resonate at specific radio frequencies determined by the size of the brain cavity. At these resonant frequencies the human head will absorb vastly more radiowave energy than it will at other nearby frequencies.
An adult's head will resonate at a frequency between 350 and 400 MHz (megahertz). Being smaller, a child's head will resonate at a higher frequency, somewhere between 600 and 850 MHz. Since each individual may have his or her own resonant frequency, a particular frequency radiowave might affect one person more than another. Consequently, testing on humans--even if people are willing to let this happen--can be rather complicated.
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Basically the human head is a resonance chamber that probably amplifies the signal. But also your body is made of water, and RF bounces off metal and water. The capacitive coupling of skin probably adds an enhancement to the effect.