15 ms·
Why does holding a key fob to your head increase its range?
- scelerat 3y agoGrabbing an FM antenna when you've got a weak signal has a similar effect
- fndragon 3y ago[dead]
- cranberryturkey 3y agoyour skull acts as an antenna
- pestatije 3y agoanybody's head range increases by holding anything to it...101 physics
- icepat 3y agoI'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.
- dijksterhuis 3y agotop gear (UK) demonstrating this in practice (potato video quality) https://www.youtube.com/watch?v=_jACSPipPSE https://www.youtube.com/watch?v=_jACSPipPSE
- deleted 3y ago[deleted]
- gnicholas 3y agoI’ve found it helps to hold my key with both hands.
- Buttons840 3y agoIt 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.
- tempestn 3y agoThat was my first thought too, but the OPs tests had the range only improving when held to the head.
- chii 3y agoi 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...
- TeMPOraL 3y agoWe 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.
- rft 3y agoThanks 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/21846630/microwaves-rf-seawater-fountain-transmits-and-receives-signals-like-an-antenna https://www.mwrf.com/technologies/embedded/systems/article/2...
- userbinator 3y agoI 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#Parasitic_elements https://en.wikipedia.org/wiki/Driven_and_parasitic_elements#...
- deleted 3y ago[deleted]
- kevin_thibedeau 3y agoMust have been the log lady's secret all along.
- rabuse 3y agoMy 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.
- deleted 3y ago[deleted]
- behnamoh 3y agoIn the movie LalaLand, they mention that this is dangerous (causing diseases). Is that true?
- justapassenger 3y ago[dead]
- acomjean 3y agoI 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-better-when-pointed-at-your-chin/35390 https://community.cartalk.com/t/does-the-remote-entry-work-b... Your phone is probably worse.
- buntz 3y agoDuring 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.
- hammock 3y agoWhy would the duration or frequency of the burst matter if RF is harmless?
- seba_dos1 3y agoWhy would the amount or the way it gets into your body matter if water is harmless?
- initplus 3y agoRF 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.
- 3y ago
- pyinstallwoes 3y agoI always thought it was because my skull acted as an antenna :P
- entropicgravity 3y agoIt's your conductive nervous system (including your brain) that is acting as a directional antenna.
- cableshaft 3y agoUsed 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.
- nsonha 3y agoMy brain could not connect to wifi the other day and the key fob trick worked!
- BobbyTables2 3y ago[dead]
- TheWoodsy 3y agoKeysight Labs did some testing on this a few years ago. https://www.youtube.com/watch?v=AjYyjQKW-pU https://www.youtube.com/watch?v=AjYyjQKW-pU
- buescher 3y agoThat's actually pretty good. Their data (https://youtu.be/AjYyjQKW-pU?t=198 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".
- nxobject 3y agoI never expected the sire of HP's test and measurement division to be posting entertaining casual YouTube content, but here I am.
- piskov 3y agoMakes one wonder about bluetooth headphones
- plugin-baby 3y agoIME Bluetooth headphone volume increases if you put them near your head
- aqfamnzc 3y agoI find this especially true when moving them close to the ears. Could it be the dished shape?
- KeplerBoy 3y agobluetooth 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.
- hakdbha 3y ago[dead]
- karol 3y agoCan we now discuss it in the context of 5g? That would be so much more interesting.
- Johnythree 3y agoA 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.
- jpk 3y agoThis 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.
- Aloha 3y agoYes - and not surprising, it's functionally acting like a ground plane.
- DeathArrow 3y agoEven 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.
- xp84 3y agoThe 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: https://imgur.com/a/1Pdfyg4 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!
- Hamuko 3y agoArm's length of the front bumper, but about 1-2 car lengths of the front door.
- maccard 3y agoMy first thought was "I wonder if the car is to scale or the fob"
- chaorace 3y agoWell, 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!
- mcv 3y agoShort 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.
- dtgriscom 3y ago> Modern cars unlock automatically if you try to open the door while the keyfob is in range Oh, no. Yet another reason not to buy a new car. (Hope it can be disabled in the preferences somewhere.) Technology trying to guess what I want is almost never a good thing. It'll get it right 80% of the time, but that last 20% is a killer, and means I'll have to monitor it carefully all the time. My aunt had an older Prius, and sometimes when she locked it and walked away it would still see the fob and unlock itself. She had to carefully sneak away from the car to make sure it stayed locked.
- seeknotfind 3y agoBecause 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
- martin-adams 3y agoI’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.
- LargeTomato 3y agoOne more anecdote, this has not consistently worked for me. Raising the height of the receiver may have an effect but I'm not sure.
- pbhjpbhj 3y agoMaybe there's a difference in resonance of the people reporting their experiences here; also differences in the frequency tuning of the fobs?
- ta8903 3y agoMaybe the one case where "you're holding it wrong" is valid advice.
- redhale 3y ago
- avalys 3y agoThis 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.
- green-salt 3y agoThanks to this trick I have saved countless hours searching parking lots
- jurassicfoxy 3y agoIt'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.
- ipython 3y agoFunny I came here to share the “chin” trick as well.
- MaXtreeM 3y agoSixty symbols (same author as Numberphile) video on this from 9 yeas ago: https://www.youtube.com/watch?v=0Uqf71muwWc https://www.youtube.com/watch?v=0Uqf71muwWc
- martijnvds 3y agoSixty Symbols did a video on this almost a decade ago: https://www.youtube.com/watch?v=0Uqf71muwWc https://www.youtube.com/watch?v=0Uqf71muwWc
- class3shock 3y agoI 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.
- risfriend 3y agoFascinated by this, going to dig deep.
- snapetom 3y agoWow, 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.
- mmaunder 3y agoNot 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.
- phendrenad2 3y agoI think this is the real answer.
- Angostura 3y agoIf that were the case, wouldn't simply holding it in your ungloved hand be sufficient?
- teeray 3y agoProbably 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.
- gorlilla 3y agoThe 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.
- HPsquared 3y agoThe same reason your phone speaker gets louder when you put it on the table.
- throwaway892238 3y agoI 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-effects-humans 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. 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.
- aaron695 3y ago[dead]
- WithinReason 3y agoAn explanation I read somewhere is that the radio waves reflect from the inside of your skull, the curvature acts as a parabolic antenna.
- eps 3y agoThat'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.
- willis936 3y agoGiven 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.
- K0balt 3y agoIt’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.
- ht85 3y agoFrom 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"
- jimnotgym 3y agoExcuse 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!
- ht85 3y agoYou are correct, wikifeet confirms it.
- elzbardico 3y agoFunny 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.
- hprotagonist 3y agoThere 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.
- johnny_canuck 3y agoI 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.
- nativeit 3y agoI 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.
- aadityaubhat 3y agoGood explanation I found on YouTube few years back - https://youtu.be/0Uqf71muwWc?si=eLDi_zvMtXJeh_WZ https://youtu.be/0Uqf71muwWc?si=eLDi_zvMtXJeh_WZ
- mypgovroom 3y agoIt doesn't
- peter_d_sherman 3y agoInteresting! >"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 https://en.wikipedia.org/wiki/Capacitive_coupling
- marcus0x62 3y agoWhen 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-40180-8EV89 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 https://en.wikipedia.org/wiki/66_block
- chaorace 3y agoThose 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
- dicroce 3y agoWhen 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...
- differentView 3y agoThe lesser known origin of Aquaman.
- 99catmaster 3y agoAm 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.
- arbitrage 3y agoHold 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.
- BoThrowAway 3y agoI'm not touching this one- I want to, but no.
- svnt 3y agoYou might try flipping the fob over
- 8bitsrule 3y agoWhen 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.
- effnorwood 3y ago[dead]
- egorfine 3y agoThis 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. Warm car in winter, yeah