In the movie LalaLand, they mention that this is dangerous (causing diseases). Is that true?
In the movie LalaLand, they mention that this is dangerous (causing diseases). Is that true?
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.
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.
Back in the early 00's when we still had analogue VHF TV signals, we wanted to watch the football world cup at school. Of course there was no cable or anything at the school and no VHF antenna and streaming was not a possibility yet so we had to be creative. We found an antenna cable and tried to manipulate the cable and use whatever as an antenna. We tried the sheet metal roofing, but that didn't work very well, we tried some metal rods and that didn't work great either. By chance we found out that if someone held the cable in one hand and leaned out of the window with their other hand stretched out we got a signal that was good enough to watch the game. Well, for everybody except the poor bastard that had to stand behind the TV halfway out the window.
Fond memories here of watching Babylon 5 on a Performa 5300 with an Apple TV Tuner Card. There was no antenna to the room with the computer, but I found that I was able to get an acceptable picture by holding the coax cable attached to the antenna input in the right way while keeping one hand attached to the central heating radiator...
A metal fork is the best antenna (among non-antennas)
So a homemade theremin?
Reminded me of discovering this when I was a kid and thought I was magic. I had forgotten about that.
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.
I read it in the sense that they would retune or reengineer it if it was discovered that holding it in a hand resulted in poorer performance - ie. they need to factor in the environment it operates in (a hand beside a body) after they design it on paper.
There are 2 limiting factors taken into account during design - regulations and peak current that the battery can supply.
The battery thing (usually a coin cell CR2032 that can supply ~13mA per spec) can be a bit mitigated with a beefy capacitor (though RF packet length and space in-between have to be appropriate for the capacitor recovery, not to brown out the system).
Usually the bigger bottleneck is the regulation, so you tune for best performance in a clean environment. Hand and body during operation are really unpredictable to model in/retune, but luckily usually adds for the better. Anyways the range of the classical RF fobs (@3xx-4xx MHz and 8xx-9xx MHZ bands) is well beyond the real world needs that the 10-20% drop of performance due to certain fob positions will make a difference. If it does, you probably have a low battery.
Next gen fobs (if they hit the mass market) are BLE and there the range performance is more critical. Dunno what will be the approach there.
What can cause problems are ornament and the mechanical key insert. It has to be extensively tested that there is no coupling with those metal parts that are close to the antenna. Problem comes sometimes when they decide to redesign a bit the keyfob without going through the tests internally (e.g. oh it's just a minor tweak of the radius of the metal ring around the fob housing...) and then the certification fails and has to be repeated (not just money, but getting the slot for it...). Some OEM might even be inclined to think they don't need a certification for such a minor change and push it to the market, making the problem worse if there is an issue.
Regarding the ornament things on fobs, there were even instances of them magnetically coupling with the wireless chargers or even immobilizers and that lead to some melting...
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.
Yes - and not surprising, it's functionally acting like a ground plane.
How does it detect the presence of a nearby human body?
OP means that while developing the radio and antenna part of the fob the engineers have adjusted the radio and antenna to work the best when in close proximity to a body. The human body has a certain effect on the radio signals, so adjusting the radio and antenna to work best while close to the human body will mean that it won't work as optimally when further away from a human body.
It doesn't detect the human body, it is just designed to work the best when it is physically close to the human body.
The scenarios being compared are:
- 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.
More likely than what? SE comments provide at least three distinct theories. IMO this one (also provided in the comments) seems fairly conclusive https://www.remcom.com/examples/keyless-entry.html
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.
This is true.
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.
Or pointing it at your head, is the same as holding it up high in the air.
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.
That was my first thought too, but the OPs tests had the range only improving when held to the head.
i suspect the torso's cavity isn't as amplifying as the liquid in your brain.
an interesting test would be to try a full bladder vs empty bladder...
We could then measure how the signal range changes as you pee, particularly with the length of the urine stream.
I'm serious. This would be an analogue to those navy experiments with shooting streams of sea water to fashion temporary antennas of arbitrary length, instead of having permanent ones that have fixed length and stick out.
Thanks for the liquid antenna pointer, I had no idea this was actually tried! Apparently not only the navy thought about this, but there are idea floating around about using liquid metal for variable length antennas.
One of the links I found: https://www.mwrf.com/technologies/embedded/systems/article/2...
I've had my fob fail to work multiple times while walking away from my car, so I take it out of my pocket and put it near my lower back and it works (even though I'm now even farther away because I'm walking).
That's slightly different though, sounds like fob went from being blocked by your body to no longer being blocked by your body.
I’ve always put the key behind my head when doing this, and can confirm, it extends the range through experimentation.
I thought for sure I’d be absorbing it with my head but I definitely get extra range.
vs holding it out at arms length but same height? Ground interference is a thing.
I can confirm that holding the remote next to the head doesn't work, but touching chin, temple or the back of the head does extend the range. This works not just with car remotes, but also with garage door openers.
Have you tried standing on one leg, and touching your nose with the free hand. Vast improvement over the amatuer technique
My favorite place (and yes I do this since I saw the Top Gear) is under the chin, pointing the fob/key upwards and opening my mouth. So it doesn't use the skull's cavity but the mouth's (or so I think/believe)
Yes, holding at same height. I did not know about ground interference! Thanks.
It’s just using the water in your body as an antenna.
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.
You can see the same effect by holding the car remote to a water bottle.
And this ^ doesn't actually work.
I know it because I specifically tested it. Went from 2L bottles and all the way to 8L jug. Nada. But the head works.
You’ve piqued my curiosity.
I will have to run more tests.
clean water isn't a great conductor - the body is a bag of dirty water...
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.
One more anecdote, this has not consistently worked for me. Raising the height of the receiver may have an effect but I'm not sure.
We need to cross analysis people across the axes of tall/short and large/small head for posterity
Maybe there's a difference in resonance of the people reporting their experiences here; also differences in the frequency tuning of the fobs?
Maybe the one case where "you're holding it wrong" is valid advice.
"Works on my skull"
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.
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!
My first thought was "I wonder if the car is to scale or the fob"
Well, it's in a 3D perspective so we have the third option of saying that they're both to scale and that the perceived size difference is a forced-perspective illusion. In that case you could actually measure the distance depicted in the diagram, though I have my doubts about how accurate they bothered to make it!
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.
If range is desirable, Tesla's, and I imagine other cars have this as well, have a cell modem and an app, so you can control it via the Internet, which is effectively infinite range. It's occasionally handy to be able to unlock the doors to let someone into the car from elsewhere in the world. Eg friend left their bag in the car but I'm not around to let them in.
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.
Arm's length of the front bumper, but about 1-2 car lengths of the front door.
Makes one wonder about bluetooth headphones
IME Bluetooth headphone volume increases if you put them near your head
bluetooth is a digital transmission. The volume is encoded in the signal, it can't get louder just because it receives a clearer signal.
Unless the reduced power consumption by the transceiver causes the battery voltage to rise noticeably.
Empirical evidence says otherwise. Bluetooth headphones on desk, can hardly hear anything. Touching my head (particularly the ears), loud and clear.
Ohh, I need to work on my sarcasm detector.
I find this especially true when moving them close to the ears. Could it be the dished shape?
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.
If that were the case, wouldn't simply holding it in your ungloved hand be sufficient?
Probably not. Position of the antenna relative to the ground plane alters the radiation pattern. That’s why you’ll see police cruisers mount their antennas dead center on the roof—it creates an omnidirectional pattern. Mounting it to one side or another causes the field to radiate more in the direction with more roof in front of it (kind of the opposite of intuition). So the remote in your hand still likely interacts with your body, but not in a controlled or desirable way.
The ground plane is typically orthogonal to the antenna. Both TX and Rx antennae will have their own 'effevtive' ground plane relative to each other at any give point in time that will effect their Tx/Rx capabilities. Add into that, parking lots are full of metal objects and typically nearby large buildings. Those, also, will change the propagation characteristics of the general environment.
There's a lot at play in open-air environments. This does seem quite easy for DIY experiments using RTL-SDRs in varying environments.
I think this is the real answer.
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.
You might try flipping the fob over
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.
I'm not touching this one- I want to, but no.
From the top answer:
1/2 m ≈ 1.5 ft
Thanks US units for the quote of the day: "Meters are for waves, feet are for antennas"
Excuse me, feet are US units??? Surely you mean feet are units that were adopted in the US... and then dropped by the rest of the world!
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.
I’ve found it helps to hold my key with both hands.
That would support the head-arm loop theory.
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.
your skull acts as an antenna
anybody's head range increases by holding anything to it...101 physics
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.
This effect 100% works, I’ve tried it many times over 20 years with many different cars.
It is best if you hold the flat side of the remote up against your chin.
It's really funny when people don't believe it though. At first glance it looks like such an obvious "you're a gullible idiot" hoax, haha.
Funny I came here to share the “chin” trick as well.
An explanation I read somewhere is that the radio waves reflect from the inside of your skull, the curvature acts as a parabolic antenna.
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.
That's a pretty dumb explanation if you pardon the bluntness. The effects shows itself regardless of how the head is turned reltive to the target.
I am disappointed to see no mention of "passive radiator" nor "parasitic element" on that page anywhere: https://en.wikipedia.org/wiki/Driven_and_parasitic_elements#...
Must have been the log lady's secret all along.
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...
1 - a wiring terminal commonly used in the telephone system. https://en.wikipedia.org/wiki/66_block
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
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.
Keysight Labs did some testing on this a few years ago. https://www.youtube.com/watch?v=AjYyjQKW-pU
I never expected the sire of HP's test and measurement division to be posting entertaining casual YouTube content, but here I am.
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.
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...)
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.
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.
Fascinated by this, going to dig deep.
My ex-girlfriend used to do this back in our teens, and I used to think she was crazy... until I started to do it. Blew my mind.
I always thought it was because my skull acted as an antenna :P
Interesting!
"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
My brain could not connect to wifi the other day and the key fob trick worked!
It doesn't
Sixty Symbols did a video on this almost a decade ago: https://www.youtube.com/watch?v=0Uqf71muwWc
Can we now discuss it in the context of 5g? That would be so much more interesting.
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.
amazing.
It's your conductive nervous system (including your brain) that is acting as a directional antenna.
top gear (UK) demonstrating this in practice (potato video quality) https://www.youtube.com/watch?v=_jACSPipPSE
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...
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.
Good explanation I found on YouTube few years back - https://youtu.be/0Uqf71muwWc?si=eLDi_zvMtXJeh_WZ
Sixty symbols (same author as Numberphile) video on this from 9 yeas ago: https://www.youtube.com/watch?v=0Uqf71muwWc
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.
The same reason your phone speaker gets louder when you put it on the table.
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.
https://community.cartalk.com/t/does-the-remote-entry-work-b...
Your phone is probably worse.
Why would the duration or frequency of the burst matter if RF is harmless?
RF is harmless below the point where it directly heats tissue.
Having a full strength cell tower transmitter inside your home is not safe due to the intensity of the transmission, it will directly heat tissue inside your body.
Would it heat tissue anymore than the Sun (in warm places) or your heater or air-conditioner set to heat already does 10x stronger?
Microwave RF that is somewhat directional behaves a lot like laser light.
If you were to step into the beam carried by a waveguide for something like a powerful TV transmitter, it will cook you through like a death ray out of science fiction. Fortunately it's not actually collimated, so just a few feet away the energy is barely enough to cook your retinas faster than your blood supply can cool them (which can cause blindness). Otherwise, yes, it's much like infrared heating effects. If infrared penetrated a few centimetres deep, anyway.
While fob frequency is microwave, isn't it also much lower energy compared to, say a microwave oven, powered by mains power to cook food?
And also the fob operating in the low 100s of Mhz, not GHz, wouldn't that make it less dangerous?
https://www.youtube.com/watch?v=yqljaKjKjd4
^ this guy literally does nothing more than lay a long wire out on the grass, and touching it instantly smokes and burns his skin
I think the distinction/point is that it's not harmful in the 'this might give you cancer' way that ionizing radiation sources will. Worst case, you get an RF burn... which is not great, but it's effects are immediate and obvious, unlike ionizing radiation which is much more insidious.
Why would the amount or the way it gets into your body matter if water is harmless?
During summer my bald head burns in the 5 minutes it takes to roll garbage to the curb.
Really doubt even phones are dosing us the way nature does.
Should we worry about a radio transmission powered by a 3 volt battery while taking on our phone?
A phone battery is 3.8 volt. No worry, right?
Good point. I don't know much about these things. Are the radio transmissions from a phone stronger? I would expect so, but don't know.
Depends. There is lots of irrational fear with this and as far as I know, no solid proof for harm, but there is extra electricity flowing in your head, because of the transmission of your phone. I don't like talking on the phone that much anyway, so I do not care so much, but if I would talk for hours, I would use a headset (also for ergonomic reasons).
But my remote contains a 12V battery /s
As true as the notion that cellphones and microwaves cause cancer.
I'm pretty sure that was a "neg".
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.