Can I unlock my car using my head?

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1:05Hello. We are going to do an experiment for crowd science today. We're going to go on a walk with my dog, Maura. Come here, Maura. Sit. That's a good girl. Maura is a championship wheat and terrier. She will do just about anything for a treat. So she's a very willing participant in this experiment.

1:29Caroline Steel:This is CrowdScience from the BBC World Service, the show that answers your science questions. I'm Caroline Steele, and the owner of today's Very Obedient Terrier is listener Doug. I'm Doug Brown, and I'm calling from Calgary, Alberta, Canada. Doug emailed into CrowdScience because he has a question about some strange behaviour from wireless keys. Keys that open something like a car or garage from a distance. or as Doug likes to call them, fobs. My question for crowd science is that I recently heard that holding a car fob to your chin will extend its operational range. And I was just wondering what the physics was that was going on with this.

2:11Caroline Steel:Interesting. Okay, so you say you heard that holding it to your chin doubles the range. Where did you hear that? It was just one of these life hacks that was talking about what you could do when your car fob battery was dying and you needed to open your car door. Oh, a useful hack. And so you thought, OK, hang on a second, I'm going to give this a go. That's correct. So Doug actually recorded himself giving this trick a try. I'm going to open the garage door, walk down the block and see how far my garage door fob actually works. OK, we're now outside. It's a gorgeous, sunny spring-like afternoon.

2:51and I'm going to walk down the neighbourhood. In our neighbourhood, each house is approximately 15 metres in width. So that'll give us a quick indication of how far we have gone before pressing the fob.

3:05Caroline Steel:First, Doug went to the very edge of the range of his wireless key, which is five houses away from his garage. We're just about there now. I'm going to push the garage door fob and make sure it works, and this will be our baseline measurements. At six houses away from his garage, which is about 90 metres, Doug pressed the button on his key to open the door. It works. I'm now going to walk down another house and try things again. Held normally in his hand, Doug's fob didn't unlock his garage door. I try it with no augmentation and it doesn't work. But then he tried his head trick. I try it on my chin.

3:50It works.

3:52Caroline Steel:Great work, Doug. We love it when CrowdScience listeners take science experiments into their own hands or heads. We'll come back to Doug and Dogmora later on in the show. But first, why on earth does holding a wireless key to your head make it more effective? I have to say I love physics, but I genuinely have no idea what's going on here. Let's start with the very basics. Keys like this can unlock garages like Doug's, as well as all sorts of other things like cars. So how exactly do wireless keys work? Right, so let's start from the beginning. So there would be a coded digital signal that is sent from the key to a receiver inside the car or the garage door system, for example.

4:37Caroline Steel:This is Dr Lina Majazi, Senior Lecturer in Wireless Communications Engineering at the University of Glasgow in Scotland. First of all, we press the button on the key fob, and after that, a small electronic circuit inside the key generates a signal called an RF signal, which just means that the signal is at radio frequency. And then the digital data, which is essentially the unlock code, is then encoded onto that signal. Now, the signal after that needs to leave the key at some point and travel through the air. You can imagine it as writing a message on a paper airplane. So the data is the message and the radio wave is the airplane carrying that message through the air from the key to the receiver.

5:23Caroline Steel:OK, so every key is sending like a unique message via this radio wave. And the car or the garage door is being like, oh, that's my message. I recognize that wave. Time for me to open. Yes, precisely. So that particular code is sent to the receiver and then the receiver checks the code. And if it matches the one stored in the system, you can imagine that there's a handshake that's happening between the transmitter and the key fob and the receiver in the car and the door would unlock. And each time, is it unique? Like, could my car key unlock another car? So the signal is totally unique to that particular car.

6:03Caroline Steel:Which is good, because that would be a problem. If I could go around unlocking or locking other people's cars, that would be a problem. Yes, indeed. Yeah, imagine it. OK, so when you press a wireless car key, it sends out a radio wave carrying a unique code. And the car's receiver interprets that code and only unlocks if it's a match. But how does the electronic circuit inside the key make a wave in the first place? So let's look inside the key fob. There is a small electronic circuit powered by the battery. That battery provides electrical energy, but the circuit converts that steady energy into a current that oscillates extremely quickly.

6:47Caroline Steel:Oscillate just means sort of current going back and forth, right? Yes. So instead of electricity flowing in one direction only, the charges in the circuit are made to move backwards and forwards millions of times per second. And when the electric charges move like this, especially when they accelerate or change direction, they produce electromagnetic waves. OK, so there's kind of a key point there, which is moving charges create waves. An analogy here is a bit like shaking a rope, right? So if you move the rope back and forth, waves travel along it. So in a similar way, when electric charges move back and forth in a circuit, they create waves in the electromagnetic field around them.

7:30And those waves are what we call radio waves and transmit out into the air through the antenna.

7:38Caroline Steel:So inside the key, there's an oscillating current, which produces a wave that leaves the key via an antenna. But what exactly is an antenna? The antenna is the part that takes that electric signal inside the key, converts it into a radio wave that can travel through space. It could be of different designs, different structures, but you can simply imagine it as a simple metal wire. Then this electric signal is converted into a radio wave that is then moved into space. An antenna can be as simple as a small coil of wire, much smaller than the antennas I'm familiar with, like the long aerial that pulls out of an old-fashioned radio, or a huge satellite dish we use to communicate with things in space.

8:25Caroline Steel:So why do we see such a range of sizes? How are the tiny antennas that fit in a wireless key so effective? Usually wireless key fobs, they operate at typical frequencies of around 300 to 400 megahertz, depending on the country. and at those frequencies the wavelength is really large, roughly around one metre. That's really big. Now a very common rule of thumb in antenna design is that it often works really well, around a quarter of a wavelength long and in some cases around a half wavelength depending on the design. So for frequencies like a car key, then an ideal antenna would actually be within tens of centimetres long.

9:09Caroline Steel:So if you want a car key with the best possible range, it will need to be about the size of a dinner plate to house the antenna, which would ideally be about 20 centimetres, or one quarter of the wavelength, where the wavelength is the distance from peak to peak. Imagine that that wouldn't fit because it needs to go into your pocket, into your hand, it needs to be small. Yeah, that would be annoying. Aha, exactly. So yes, there's a compromise over here. OK, so but in this situation with Doug with his garage key, or if you're trying to open a car using a wireless key, how far is that radio wave travelling?

9:43For car fobs, I would say something around 5 to 20 metres is a good estimate. And of course, it depends on battery. So a weaker battery can reduce that range because if the battery is weak, it means that the electronics inside that key is generating a weaker signal from the start altogether. And this means, naturally, magnetic waves leaving the antenna carries less energy because they were originally generated using a weaker signal. So the range would be affected by the battery itself.

10:19Caroline Steel:Which brings us back to listener Doug's hack, holding a garage key to your head to extend its range, which could be especially helpful if the battery is low. Now, any good science experiment needs lots of data. Can Doug's findings be replicated? I think it's time to give this trick a go myself. That's coming up next. This is summer at its peak. Whole Foods Market Summer Fruit Fest is your invitation to eat the season. Fresh, organic and bursting with flavour. Start your day with peaches and organic blueberries and yogurt. Build a grazing board with fresh fruit, prosciutto and artisanal cheese.

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11:46Caroline Steel:You're listening to CrowdScience from the BBC World Service, the show that investigates your questions about the world around us. this week we're answering a question from listener doug in canada he wants to know why holding a wireless key to your head increases its range so i'm with producer tom i'm standing outside and i am 88 meters away from the car it's not opening if i just hold the key in my hand now it's not working at 87 this is not a precise science is it okay so it's not working at 87 meters let me try it on my chin yes okay so that works right i'm going to keep trying with my chin okay so it's working at 87 it's working at 88 i look what incredibly mad it's working at 89 it's working at 90 working at 91

12:51Caroline Steel:it's working at 92 it's not working at 93 so we improved its range by was it five meters 87 to 92 five meters yeah okay so it worked at 87 without my head and we got it to 92 with my head so my head improved it by five meters that's not a doug level success is it it's a mild success which is a shame but you know my head isn't Doug's head so what is going on inside our heads are they magic is Doug's head particularly magic let's go back to Lina so the idea here is that the human body is becoming part of the antenna system your body interacts with the electromagnetic field around the key's antenna and that's because the body contains a large amount of water which is made of H2O or otherwise hydrogen and oxygen atoms bound together.

13:45And in biological tissues, that water also contains many dissolved salts. So you can think of sodium, potassium, chloride. So because of this composition, our bodies, they have certain electrical properties, such as electrical conductivity, meaning that electric charges can move through our body to

14:07Caroline Steel:some extent. Is that because these ions and salts act like a kind of moving current, like in the key? Yes, indeed. And because of that, it can influence the electromagnetic field generated by the antenna. So our bodies are conductors, and that means they can act as antennas, like the loops of copper wire inside a wireless key. And for some reason, human-sized antenna are remarkably good at extending the range of a wireless key. But why? Here's another electrical engineer who knows this trick well. It's something I use in my course on antennas where I introduce this specific effect. This is Guy Vandenbosch, professor of electromagnetic radiation at KU Leuven University in Belgium.

14:56Caroline Steel:And he thinks there's a key concept we need to understand. An antenna has what we call a radiation pattern. An antenna doesn't transmit power equally in all directions. It depends on how the radio waves combine as they spread out through space. In some directions, they line up and reinforce each other, making the signal strong. In other directions, they cancel each other out, so almost no power gets through. The result is a pattern of peaks and dead zones around the quay, which we call a radiation pattern. A radiation pattern is telling you how much power is transmitted in each direction in space.

15:34and it's the interference of all the little waves by the little currents everywhere in the antenna that determine how that radiation pattern in space behaves. But it's the shape of the antenna that actually defines the directivity by which it radiates. Directivity meaning sending more power in one very specific direction. And there is a general rule, the larger the antenna, the higher the directivity you can reach. For example, with your key or a remote control, you cannot reach a very high directivity. For that, you need a bigger thing.

16:07Caroline Steel:A bigger thing, which in listener Doug's case, is the human body. You get actually two components of a single wave. One component is created by the key itself, the antenna in the key. But you have to add the wave, which is also created by the currents flowing in your body, and they oscillate. The whole of your body is becoming part of the antenna structure. And since your body is much larger than the key on its own, well, you have the possibility, It's not guaranteed, but you have the possibility that you have a higher directivity, that you send power in a more specific single direction. Lina has a good analogy for what happens when this works.

16:46So you can imagine holding a flashlight. Instead of scattering the energy randomly, what happens is that we are focusing that energy towards a specific direction, meaning a little more of the existing signal is reaching to the car. And that's because the way they interact, the way the signals are combined, they become constructive.

17:07Caroline Steel:This is an example of constructive interference. Waves from the key and the human head combine and the radiation pattern changes. To use Lena's analogy, the key goes from behaving like a light bulb that shines dimly in all directions to behaving more like a torch or a flashlight that sends a stronger beam of energy in a particular direction. So these waves, they add together and they locally increase the signal strength at the receiver. So we are not creating more power. We are just using that existing power more effectively. It's a phenomenon that works surprisingly well with human heads. But what about other parts of our body?

17:49Caroline Steel:Here's Guy Vandenbosch again. It will not work everywhere. It will depend very much on the circumstances where you exactly put your key. The hard thing is it's hard to predict exactly what is going to happen. So and that's why you do experiments. Yeah, that's why Doug does what he does. Yes. Doug and his dog Mora have been testing whether holding the key to other body parts, not just Doug's head, also increases how far away from his garage his key will unlock the door. Let's join them once again on the streets of Calgary in Alberta, Canada. This time, they started 75 metres away from the house.

18:29I hold it to my elbow. It works. I hold it to my abdomen. It works. OK, Maura, sit. I hold it to Maura's head and it still works.

18:41Caroline Steel:At 75 metres, Doug's key opened his garage door when he held it in his hand in the usual way. And it also worked wherever he held the key to on his body. So his abdomen, head and Maura's head too. Then they walked to the next house, which is 90 metres from Doug's garage. I try it with no augmentation and it doesn't work. I try it on my chin, it works. I try it on my elbow, it works. I try it on my abdomen, it works. Maura, sit. I tried on Maura and it no longer works. OK, so Maura's head was out of the game at 90 metres, but the key still worked when Doug held it to his head, elbow and abdomen.

19:32Caroline Steel:But Doug didn't stop there. So now a total of seven house away from the garage. That's 105 metres. I hold it to my chin, it works. I hold it to my elbow, it doesn't work. I hold it to my abdomen. It doesn't work. OK, I go ten houses away and it no longer works. So Doug got the key to work up to 150 metres from his garage. That's pretty impressive. You see that I've just about got a doubling of range by holding the garage door fob to my chin. So not all body parts are made equal. Doug's head performs far better than his elbow. And not all heads are made equal either. Doug's head is a far better range extender than my head or his dog Maura's head.

20:29Caroline Steel:Let's talk to our professor of electromagnetic radiation, Guy, again. So Doug has tried this with his head. He's also tried with his dog's head and found that it didn't work. what do you think is going on there? It does not work with a poodle. But is that because a poodle is too insulating?

20:53No, that's a joke, Caroline. Okay. No, the principle is exactly the same, but the shape of your dog is not the same as the shape of a human being, a human head. So your antenna topology is different, which creates a different radiation pattern. And this is a, it's kind of a coincidence that you get a higher directivity in a certain direction that you want. Yeah. And I'm sure that you did not try all directions with your elbow. If you start by, for example, putting the key on your head and oh, it starts to work, but I guess that you were looking at your car.

21:30Caroline Steel:Yes. So that's a coincidence that exactly in that direction, you had a higher directivity. so I guess when you did the test with your elbow you still looked at your car yes I think Doug did still looked at his garage door yeah yes yes you still but there is no guarantee that that topology has its uh let's say largest directivity in the same direction it can also be in a different direction actually you have to start rotating with your body and then even like this to see what direction is now the most optimal direction if you put the car key on your elbow. And it's possible that you find a direction which is even better than putting it on your head.

22:12I don't know.

22:14Caroline Steel:So experiment not complete. Yes, got to rotate. Yeah, indeed. Well, thanks to Guy standing up and doing a twirl for me, I now know exactly how I should rotate to test this for myself. okay so i'm back outside i'm standing 88 meters away from the car and here the key on its own in my hand isn't unlocking the car if i hold it to my elbow that isn't unlocking the car either okay so let's test guy's idea could it be that if i face in a different direction i can change or improve the radiation pattern so that the car does unlock? Or will I just send the signal into the bushes? OK, so I'm holding the key to my elbow.

22:59Caroline Steel:I'm going to turn 90 degrees clockwise. So let's say I'm facing 12 o 'clock now. I'm going to turn to 3 o 'clock. That doesn't work. OK, I'm now going to face 6 o 'clock, which definitely feels like it shouldn't work. So I'm literally facing away, holding the key to my elbow, with my body facing away from the car. Is that working? It worked! It worked! What? Okay, so... Do that again, see if it's a one-on, see if it works twice. Okay, so I'm holding it against my elbow at six o 'clock. There you go. Oh, my gosh. Okay. I'm going to turn another 90 degrees for sake of completeness. So now I'm at nine o 'clock and it's not working.

23:40Caroline Steel:So it works at six o 'clock, but it doesn't work at any other time. And that must just be to do with the shape of my body and how my elbow is interacting with the waves coming out of the key. I basically am changing the interference pattern in a way that is favourable for opening the car facing that direction. It's hard to think it's not coincidence. It is hard. It's just mad, isn't it? OK, right. I need to give this car and car key back to the very generous owner who has lent it to me. And we're nearly at the end of the show. But first, we've got one last quick question from listener Doug. One of the things I was wondering about, if it works for a car fob, you know, would it work for your mobile?