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Why does holding a key fob to your head increase its range?

physics.stackexchange.com

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Re: Why does holding a key fob to your head increase its range?

#131

Post by eitally »

xp84 wrote: post #43

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: 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 b…

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.

Re: Why does holding a key fob to your head increase its range?

#132

Post by eichin »

ratg13 wrote: post #127
eps wrote: post #85

Earlier quoted context omitted.

> 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...

Re: Why does holding a key fob to your head increase its range?

#133

Post by pbhjpbhj »

martin-adams wrote: post #48
seeknotfind wrote: post #46

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.

Maybe there's a difference in resonance of the people reporting their experiences here; also differences in the frequency tuning of the fobs?

Re: Why does holding a key fob to your head increase its range?

#135

Post by fragmede »

eitally wrote: post #131
xp84 wrote: post #43

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: 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 b…

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.

Re: Why does holding a key fob to your head increase its range?

#136

Post by arbitrage »

99catmaster wrote: post #134

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.

Re: Why does holding a key fob to your head increase its range?

#137

Post by BoThrowAway »

99catmaster wrote: post #134

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'm not touching this one- I want to, but no.

Re: Why does holding a key fob to your head increase its range?

#138

Post by playingalong »

Thlom wrote: post #67
DeathArrow wrote: post #50

Earlier quoted context omitted.

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…

A metal fork is the best antenna (among non-antennas)

Re: Why does holding a key fob to your head increase its range?

#139

Post by svnt »

99catmaster wrote: post #134

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

Re: Why does holding a key fob to your head increase its range?

#140

Post by sushisource »

Buttons840 wrote: post #6

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 camp…

> 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.

I cannot wait to trick someone into doing this

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