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.
If however you tested it with the fob somewhat isolated it would then be out of tune.
eg in the factory it would be tuned at a set distance from a "dummy body".
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.
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.
This reminds me of a class in college where one project was to make a waveguide WiFi antenna. You know the ones; often built out of a Pringles can.
On the day the project was due, we each demo'd our antennas and the instructor recorded their range, SNR, etc. Most in the class followed the Pringles can tutorials, but I was always kinda extra. So I used some kind of roof flashing coiled into a cylinder to get the length and radius tuned just right, and I fashioned a comfy handle to aim it using some scrap aluminum flat, and round wood stock.
Mine did really well, but it also had the widest variance in performance. We figured out that my wood handle could be held in a way in which you didn't actually touch any metal, but if you put your thumb up on the aluminum part of the handle, it instantly got way better SNR!
The instructor told us that touching the housing improved the quality of the ground because the capacitance of our meat acts like a short at those high frequencies.
Not really - antenna is tuned to the maximum allowed emission power per local regulations (e.g. big differences between EU, US and JPN regulations).
Certification tests do not include any human handling, since it's really unpredictable and varies.
Therefore, tests are just the fob with a (per specifications) positioned Rx antenna (highly controlled environment).
BTW similar effect is observed with the fob being next to the bottle of water.
There are peer reviewed studies on these topics, that my RF engineer shared with me when I asked him way back about it, but are heavy on the RF/antenna theory, beyond my understanding.
Even simpler, tune in an FM radio and move your hand near the antenna. It will sound better or worse depending on your hand position and how close it is to the antenna.
You might be right about this, it makes sense. So standing on your tippytoes with the remote-arm stretched out to try and get better range is actually counter productive. Take 2 steps closer, and hold the remote close to your body.
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:
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!
Short range isn't necessarily bad. Modern cars unlock automatically if you try to open the door while the keyfob is in range, so long range could mean someone could unlock your car while you're out of sight.
I don't know if that system uses the same range as when you press the button on the keyfob, but I have read about a hack (probably here) where thieves used a transmitter to extend the range of both the car and the keyfob to unlock the car while the owner is out of sight. That's easier to do the longer the range is.
I had a 2001 GTI and it similarly only reliably worked within probably 25' of the vehicle. In contrast, my 2017 F150 fob works as much as 150-200' from the vehicle. I tremendously appreciate this, especially with remote start to warm it in the winter.
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.
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: https://www.grainger.com/product/EXTECH-Tone-and-Probe-Kit-4...
Those tone probes are so fun to play with! I highly recommend anyone with a spare $15 to grab a cheapo model and just... run around the home with it. It's an enlightening experience to actually perceive with your own ears the normally invisible world of EM radiation
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.
That's actually pretty good. Their data (https://youtu.be/AjYyjQKW-pU?t=198) is consistent with my experience: +/- 6 dB or more depending on who is holding the remote and how they hold it. Range checks are not very reproducible and if you start worrying about reproducibility your time is better spent setting up a basic outdoor 3m test if you don't have a chamber. Most of the "hold to your chin" effect is just "try holding it a different way".
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.
I still use this trick today to find my car when I park somewhere I am unfamiliar with.
I just had to tip my cap. I worked as an imaging clerk for Copart Auto Auctions about 18-years ago. My job was more about putting the images on the website (and ordering new photos if they weren’t to-spec, or if there was visible gore—it being an insurance auction), but I have an intimate awareness of your experience. It was an interesting, if poorly paid, job experience.
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
I’ve been using this trick for many years. Things like when in a car park and trying to confirm I’ve locked my car at some distance, this has worked. It’s been pretty reliable for me.
I typically press it firmly against my chin, and I have observed increased range many times (including testing this trick explicitly with a few different fobs a few years ago out of curiosity). Try pressing more firmly, or rotating the fob.
I too have been using this trick for many years on many cars since first seeing it done by Clarkson on Top Gear (circa 2006 IIRC and linked in the PSE question). I still baffle people with the considerable amount of extra range it can achieve. Half a football pitch was probably the best example I got on a 2008 Nissan Qashqai.
It also works holding it near your torso, don't have to use your head.
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.
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.
Funny how everybody readily accepts the metric system for measuring radio wavelengths without complaints. Even the most hardcore traditionalist ham radio operator in America never complains about naming bands with meters.
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 can imagine you may also try to raise your hands to get less ground interference, at which point it would not be inappropriate to invoke the power of Greyskull.
I was looking to see if someone had posted this, as it was what I immediately thought of when I saw the title. Lovely video, wild to think it's been that long since it's release.
Wow, I first heard about this in the early 90's in high school! I was told to hold it under your chin. It seemed 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.
>"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 couple to RF sources capacitively."
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.
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.
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.
Hold the fob under and in contact with your chin and aim your face at your car. The beam gets focused in a specific direction when you're using your head to amplify the signal. This is how you get improved distance with your head. Your skull is not an isotropic resonant emitter. The signal ends up beam-shaped.
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.
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.
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.
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.
Given the conductance of flesh and the frequencies at question the skin depth would only be a few cm at most. The RF energy never makes it through the brain.
I've started using a HAT running the TINFOIL distribution, then I've configured ingress with request token validation. I bill everyone around me on a per-request basis for UNLOCK calls to their car. I've found the system works pretty well at keeping unwanted GET requests to my MIND database by various bad actors.
https://www.youtube.com/watch?v=w5SRH6Ac1LI&t=25s Love that movie. I didn't remember that so I found the scene. The character's joking / trying to mess with the other person. "You gotta put that thing to your chin. It makes your head into an antenna, so... I think it gives you cancer but you find your car faster. I mean, you don't live as long but you get where you're going quicker so it all evens out. Just a suggestion." At 5:15 in that video she tries it and it works.
I suspect not. Its a short burst of rf and not done very frequently. (I use this technque with an key fob near an open mouth probably 4 times a year.. Thanks Car talk.
Johnythree|2 years ago
If however you tested it with the fob somewhat isolated it would then be out of tune.
eg in the factory it would be tuned at a set distance from a "dummy body".
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.
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.
jpk|2 years ago
On the day the project was due, we each demo'd our antennas and the instructor recorded their range, SNR, etc. Most in the class followed the Pringles can tutorials, but I was always kinda extra. So I used some kind of roof flashing coiled into a cylinder to get the length and radius tuned just right, and I fashioned a comfy handle to aim it using some scrap aluminum flat, and round wood stock.
Mine did really well, but it also had the widest variance in performance. We figured out that my wood handle could be held in a way in which you didn't actually touch any metal, but if you put your thumb up on the aluminum part of the handle, it instantly got way better SNR!
The instructor told us that touching the housing improved the quality of the ground because the capacitance of our meat acts like a short at those high frequencies.
wallaBBB|2 years ago
BTW similar effect is observed with the fob being next to the bottle of water. There are peer reviewed studies on these topics, that my RF engineer shared with me when I asked him way back about it, but are heavy on the RF/antenna theory, beyond my understanding.
puzzlingcaptcha|2 years ago
yunohn|2 years ago
- Fob in hand
- Fob in hand, held against head
Both of these already fulfill your “near body” requirement. Your point around tuning would not explain the specific difference being questioned.
DeathArrow|2 years ago
beAbU|2 years ago
andyjohnson0|2 years ago
hulitu|2 years ago
This is true.
b112|2 years ago
dicroce|2 years ago
differentView|2 years ago
xp84|2 years ago
https://imgur.com/a/1Pdfyg4
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!
mcv|2 years ago
I don't know if that system uses the same range as when you press the button on the keyfob, but I have read about a hack (probably here) where thieves used a transmitter to extend the range of both the car and the keyfob to unlock the car while the owner is out of sight. That's easier to do the longer the range is.
eitally|2 years ago
maccard|2 years ago
Hamuko|2 years ago
marcus0x62|2 years ago
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: https://www.grainger.com/product/EXTECH-Tone-and-Probe-Kit-4...
1 - a wiring terminal commonly used in the telephone system. https://en.wikipedia.org/wiki/66_block
chaorace|2 years ago
avalys|2 years ago
It is best if you hold the flat side of the remote up against your chin.
jurassicfoxy|2 years ago
green-salt|2 years ago
ipython|2 years ago
mmaunder|2 years ago
Angostura|2 years ago
phendrenad2|2 years ago
TheWoodsy|2 years ago
buescher|2 years ago
nxobject|2 years ago
johnny_canuck|2 years ago
I still use this trick today to find my car when I park somewhere I am unfamiliar with.
nativeit|2 years ago
seeknotfind|2 years ago
martin-adams|2 years ago
redhale|2 years ago
I typically press it firmly against my chin, and I have observed increased range many times (including testing this trick explicitly with a few different fobs a few years ago out of curiosity). Try pressing more firmly, or rotating the fob.
ta8903|2 years ago
abrugsch|2 years ago
Buttons840|2 years ago
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.
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.
tempestn|2 years ago
ratg13|2 years ago
You can see the same effect by holding the car remote to a water bottle.
You’ll notice the water bottle gives you about the same extended range as your head.
ace2358|2 years ago
I thought for sure I’d be absorbing it with my head but I definitely get extra range.
sushisource|2 years ago
I cannot wait to trick someone into doing this
dijksterhuis|2 years ago
unknown|2 years ago
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MaXtreeM|2 years ago
aadityaubhat|2 years ago
ht85|2 years ago
> 1/2 m ≈ 1.5 ft
Thanks US units for the quote of the day: "Meters are for waves, feet are for antennas"
jimnotgym|2 years ago
elzbardico|2 years ago
K0balt|2 years ago
rabuse|2 years ago
userbinator|2 years ago
unknown|2 years ago
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kevin_thibedeau|2 years ago
gnicholas|2 years ago
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tempestn|2 years ago
martijnvds|2 years ago
class3shock|2 years ago
snapetom|2 years ago
peter_d_sherman|2 years ago
>"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 couple to RF sources capacitively."
Related: Capacative Coupling: https://en.wikipedia.org/wiki/Capacitive_coupling
cableshaft|2 years ago
Always assumed it just kind of turned my body into an extra large antenna. Probably works for a key fob in a similar way.
piskov|2 years ago
plugin-baby|2 years ago
egorfine|2 years ago
Warm car in winter, yeah
99catmaster|2 years ago
arbitrage|2 years ago
BoThrowAway|2 years ago
svnt|2 years ago
hprotagonist|2 years ago
amazing.
karol|2 years ago
8bitsrule|2 years ago
HPsquared|2 years ago
throwaway892238|2 years ago
Ha, found some (kind of) evidence:
Radiowave Effects on Humans - March 28, 1980 / T. Neil Davis (https://www.gi.alaska.edu/alaska-science-forum/radiowave-eff...)
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.WithinReason|2 years ago
eps|2 years ago
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Buttons840|2 years ago
acomjean|2 years ago
https://community.cartalk.com/t/does-the-remote-entry-work-b...
Your phone is probably worse.
userbinator|2 years ago
havblue|2 years ago
justapassenger|2 years ago
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entropicgravity|2 years ago