How does Bluetooth work?

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1:04Are you ready? I'm ready. OK. OK, go. Welcome to CrowdScience from the BBC World Service, the show that answers your science questions. I'm Caroline Steele, and I'm standing in a barn in Switzerland, watching two scientists run up a rickety ladder to gather some very precious cargo. So we have the four juvenile owls now here in our clothes bags, and we will now start to measure them and detect them. Oh my gosh, so in that space of time, like a minute, you caught four owls. Baby owls. And you are carrying three dead rodents? Yeah, exactly. So that's their food reserve, yeah. So we will now determine the species, measure them, weight them, so we just have a rough idea of what they eat.

1:56We're here thanks to a question from one of you, which you're probably going to think has nothing to do with owls. But stick with me, all will become clear later in the show. This week's listener happens to live quite close to home, so we jumped on a train to meet her in person. My name is Rachel. I live in Cambridge in the UK. My question for CrowdScience is, how does Bluetooth work? Was there any particular moment where you thought of this question? Yeah, so on my commute to work, I cycle through the fields in Cambridge and listen to a podcast or some music along my journey. And I was just wondering how does my phone connect to a device like my headphones and transmit such a clear signal?

2:37We're often in a room with multiple people that they've connected to their headphones. And how do the devices not get their metaphorical wires crossed? Yes, you never accidentally sort of tune into someone else's music, do you? Well, I think we need to ask an expert. I agree. which we conveniently happen to be sat in the living room of an expert because unusually for crowd science we've managed to get everyone together in one space so could you introduce yourself please I'm William Webb I'm a telecoms expert and I've been working for 35 years now in the world of mobile communications so I've actually lived through the whole process of the invention of Bluetooth and I can certainly remember a time when people thought it was just a crazy idea and would never catch on and never be used.

3:22So it's great to be sat here talking about it now. My first memory of Bluetooth is sending ringtones to my friends at school, which at the time felt incredibly futuristic. Now today, ringtones have obviously gone out of fashion, but Bluetooth certainly hasn't. I use it to send photos, to type on my wireless keyboard and, like listener Rachel, to listen to podcasts. And all of that without a single wire. So how does Bluetooth actually work? So if we take the example that you mentioned of Bluetooth working with your headset, playing some music or a podcast whilst just cycling along, what's actually happening here is first of all, the phone itself is getting that content.

4:07It's then transmitting a radio signal from a Bluetooth chip, a special Bluetooth chip on the phone. And that radio signal travels in all directions including towards your headphones and that radio signal is being what's called modulated it's being changed by the phone in a way that reflects the music so the music will be digitally stored it will be a sequence of ones and zeros and what in essence happens is that radio signal will be made slightly louder for a one slightly weaker for a zero this signal will travel to your headphones they have a little antenna and then they'll be able to notice it getting louder and weaker and they'll turn that back into ones and zeros and then they need to turn that into actual music and then you hear it in your ears so that in a nutshell is how it all works but of course there's a lot more to it than that okay so let's go through that step by step so you said that bluetooth uses radio waves to send information can you explain how it does that exactly yeah so radio waves are actually something that's called electromagnetic waves and in fact light is part of the electromagnetic spectrum.

5:12So radio waves are in fact just a lower frequency version of light and frequency it's how many waves you see in a particular period of time. So if you imagine waves crashing on a beach if you had one every 10 seconds that might be a low frequency of waves but if you had 10 every second that would be a much higher frequency of waves and you get the same thing in radio waves there's a wide range of different frequencies. Why if they're transmitting radio waves why do you never sort of accidentally pick up some bluetooth when you're tuning a radio to a certain frequency so every single use of radio and there are thousands of them television and radio and cellular and so on is allocated its own little bit of the radio spectrum and therefore they don't interfere with each other if you go back to the old days of tuning a radio with a dial that tuning range would be well below as it turns out it's a much lower frequency than is used by Bluetooth.

6:05So that radio would never get up to the Bluetooth frequency, which is 2.45 gigahertz, which is 2.4 billion waveforms per second. So Bluetooth sends information using radio waves of a specific frequency. But why did the engineers behind it choose 2.4 billion waves per second? There's a lot of history to that, which is actually quite interesting. And in fact, we'll head through to the kitchen where we can pick up on some of that because it relates to microwave ovens. Okay, you're going to show us your microwave? William takes us into his kitchen to try a little experiment. So what has this microwave got to do with Bluetooth?

6:46So microwaves actually use exactly the same frequency as Bluetooth. In fact, a microwave is actually a very powerful radio transmitter, and nothing more than that. And it blasts your food with radio waves. And it does so at a particular frequency. And that frequency 2.4 gigahertz or 2.4 billion waveforms per second is exactly the same frequency that we use for bluetooth and and indeed the reason that bluetooth uses it is because way back when microwaves first started to be thought about people thought well actually it's going to create interference the radio signals will leak out a little bit from the microwaves that will make them fairly useless for other purposes and so it became known as junk spectrum and that meant that anybody could actually do anything they wanted with it and so people started to experiment initially with wi-fi and then eventually with bluetooth in those bands because they were available free to use and so actually it was just a very convenient place to drop in bluetooth so in fact the microwave oven in a strange way is the reason that we use those particular frequency bands for bluetooth that's so interesting so if i sort of listen to music using bluetooth headphones next to a microwave does it interfere at all so it will depend quite how much it leaks so the microwave oven is about a million times more powerful than your bluetooth transmitter in your in your handset so if only one millionth of the signal gets out of the oven that's enough to cause some issues with your headset So let's put that to the test.

8:19William places a cup of water in the microwave, as you should never run them empty, while listener Rachel and I, along with this episode's producer Anand, start streaming an episode of CrowdScience through a Bluetooth speaker. And as soon as the microwave starts, you can hear it scrambling the signal. Oh, it's stopping working. I think Jack is here. And this week we're devoting an important topic to a topic that I'm curious about. Oh yeah, it's quite upsetting. If you have got in touch asking about the science behind itching and scratching. Magic! That did actually really work. That is the sensation.

8:58As soon as the microwave stops, the audio begins playing clearly. Fun fact, this is also the reason why Bluetooth doesn't work very well underwater, which means we don't yet have underwater Bluetooth headphones. as the 2.4 gigahertz frequency used by microwave ovens, and therefore Bluetooth, is designed to be absorbed by water so it can heat up your food. It's funny to think that this chunk of the electromagnetic spectrum was once thought of as junk. But it's a good thing that it was, as it meant experimental engineers in the 90s could play around with it. Okay, I'm Jaap Hartgen. I am based in the Netherlands.

9:39I have a wife and three children. And my wife always says, well, we have a fourth child as well, and that is Bluetooth. Jaap is the actual inventor of Bluetooth. I was asked to come up with some kind of new technology that could make things around the mobile phone wireless. So no more cables and they would just seamlessly connect to each other. What year was this, roughly? When was this happening? Yeah, that was in the summer of 1994. 1994. That's when I was born. Well, you're born at the same time as my son and the technology. Where did the name Bluetooth come from? Back in like 950 AD, there was this Danish king.

10:23He lived in Jelling, a small town in Denmark. And the guy was called Blotand, which is Swedish for Bluetooth. And why was he called Bluetooth? Well, maybe he had the blue teeth because of rotten teeth or because he liked blueberries. So we use Bluetooth all the time for a product name. And then two years later, we went worldwide to launch the system. Then we didn't have a really commercial name. So Bluetooth was stuck and it was never changed anymore. So it comes from a Danish king from thousands of years ago. Right, a Viking king. And we made a little bit of a story around it because he spread out Christianity in the Scandinavian world, in Norway, Sweden, Denmark.

11:09And then we said, OK, instead of fighting each other, he made the people communicate with each other. And that's what Bluto does as well. And what about the logo, which to me is sort of crisscrossing triangles or to me it looks like a bow tie on its side? Right. And the logo, yeah, it actually consists of two parts. And it comes from the rune alphabet. One part is really a B, B from Bluetooth. But actually his first name is Harald. And Harald in the rune alphabet is written as a pole with an X. So if you have a pole and an X and you merge that with the B, then you get the logo which you see today.

11:50Who knew the Bluetooth logo is actually a hidden set of initials? It's made by combining two runes, letters from an ancient Scandinavian alphabet. An H, which is represented by a cross with a vertical line through the middle, and a triangular capital B laid on top. So back in the summer of 1994, did Jarp expect Bluetooth to really take off? No, no, no. I was a happy engineer just working with new scientific challenges. but then on a certain moment in 2006 I read an article and it said okay there are one billion Bluetooth devices shipped and then I thought oh wait a minute this is something serious this will not go in anymore and I think there are like six or seven billion devices every year shipped now that's so many devices oh my gosh but also some years ago I bought a sauna and the sauna had Bluetooth inside so I can listen to podcasts while in the sauna.

12:54That's amazing. Yeah, that's amazing. I never have imagined that. Oh, to have a Bluetooth sauna. So far, we've looked at the basics of how Bluetooth sends information through the air and some of the history of how it was invented. But we started the show collecting some baby owls. Now, you might understandably be wondering where they fit in. 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 flavor. 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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14:23you're listening to crowd science from the bbc world service and in this episode we're interested in how you're listening do you absorb answers to your science questions in your own personal bluetooth sauna like yarp do you listen via an old-fashioned radio or perhaps like listener Rachel, you're hearing this through a pair of wireless headphones. Rachel wants to know how her Bluetooth headphones work. But there are, of course, lots of other uses of Bluetooth out there, including a particular type of device that has really taken off in the last few years. Tracking tags. You might have used them yourself.

15:02You can attach them to your keys, your luggage, or in my case, my cat. And they rely on a new flavour of Bluetooth, which makes it incredibly easy to work out where something is. So these tags use a new incarnation of this technology called Bluetooth Low Energy. This is Damien Farine. They effectively send a signal out every couple of seconds and this signal is then picked up by other devices, almost any electrical device now that has Bluetooth capability. They take the location of the device and then they send that to the cloud. That's so interesting. I didn't realise that tags were completely dependent on the phones around them.

15:43Do you not kind of need permission from the phone user? It's actually not just phones. Firstly, it's smartwatches and anything that has a GPS on it. But it's done sort of behind the scenes. So it's all completely anonymous. And it's all encrypted as well, the information. So there's no real way of knowing who the phone was, what the phone was doing or anything like that. Damien has been working on Bluetooth low-energy tags as part of a research project at the Australian National University. But he's not a telecommunications engineer. He's an ecologist looking into movement patterns of different birds.

16:21The most common way that people do this now is they get these GPS tags and the tag itself records the location of the bird. We face a whole bunch of different trade-offs when dealing with this kind of hardware because it's quite energy intensive. and so you have to have a big battery and that puts on a lot of weight. So, you know, we have to either shrink the battery. So one way we've been getting around that is with solar panels, but then that increases the cost of the tags. So some of these tags cost, you know,£1 ,000 or£1 ,500 or something per tag. But Damien has figured out a way around all of these problems, tags that use Bluetooth.

16:56These tags themselves, they don't have any GPS on them. They don't have almost any hardware, just this tiny little low-powered Bluetooth chip. It allows us to basically farm out the whole processing energetic needs to the phones that are receiving the signal as opposed to having to do it specifically on the tag itself. One very small battery now can last for two or even three years on a tag. So this is really made possible by the fact that every phone has Bluetooth on it. These little tags piggyback on the power and Bluetooth capability of nearby devices, which has opened up a whole new world of possibilities.

17:34You can now track tiny birds like robins that would have been too small to put GPS tags on. And because Bluetooth tags are cheaper, scientists can afford to monitor a whole group of animals rather than just one or two individuals. Of course, there are limitations. The animals have to live fairly close to humans with Bluetooth devices. But scientists around the world are already putting Damien's tags to work. And we went to meet some of them in the Swiss countryside by the side of a road, in the shadow of a giant former tobacco barn. I'm Bettina Almazy. I'm a biologist working at the Swiss Ornithological Institute in Sempach for more than 20 years.

18:14And I'm doing research on barn owls. We heard Bettina and her team capturing four baby barn owls hiding in the roof rafters at the start of the show. It's part of a research project tracking juvenile owls. So we want to understand where the juvenile barn owls go to when they leave the family group. Because they stay together for about one month after they are able to fly. During this time they learn to hunt and then the parents do not feed them anymore and they are on their own and they have to search for their own breeding site. They can go quite far. Some are staying in the area, but others are going to Germany, to France, in all directions.

18:57This project on juvenile dispersal I started basically with my PhD back in 2004, like more than 20 years ago. We used traditional radio tags, which just sent out a beep signal and we had hand-hold antennas to follow the owls. This works quite well for the owls who stay in the regions but about one third of the barn owls they disperse further and we just lose them. Then we tried to use GPS. The GPS devices they get smaller and smaller and smaller but they still use a lot of battery power and with night active barn owls we cannot use solar panels and now suddenly in 2026 we have this exciting new device which uses the bluetooth to get locations this is the first season that patina and her team have used these tags i'm phd student at the swiss ornithological institute these are the the tags we received from damien farin well they're tiny i mean that's sort of the size of a coin right it's black and And you can see a tiny circuit board on the tag, and it's got a little chip on it.

20:09It's very small. It's about 7 grams. If an owl is 300 grams, that's a bit between 2 % and 3 % of the body weight, so that's really not much. How do you attach these tags to the owls? We have 3D-printed cases where we can place them inside. We close it with a leak. We glue it nicely together. and then we have these rubber bands that we then put in a leg loop style around the owl. Are you basically turning it into a little backpack? A little backpack but around the legs, not the wings. Now it's time to fit the backpacks and for me to get my first glimpse of one of the birds. Oh my goodness me, it's a baby owl!

20:53Hey, it's okay. Oh my goodness me. Oh, little poop. Fair enough. Oh, my God. Oh, it's so cute. It's like, excuse me, I was napping. Do you mind? But it doesn't seem too cross at you. No, they're relatively easy compared to other birds to measure them and handle them. I'm surprised by how relaxed the owls seem to be when they're being handled. Field assistant Margarita is the first to attach a tag. So I'm placing the tag on the back of the owl, and then I will be careful to pass the band right over the knee and underneath the leg, but being careful to not take the wing with me, so they can flap and fly easily.

21:42Do you think they mind wearing the tags? I think after a while they stop realizing. In the beginning, of course, it probably feels a bit weird, but after a while they will not notice anymore. And as we've seen, it does not affect the survival. and after two years they should fall off by themselves so that it doesn't stay on the whole life. And now we check that he can flap and... It goes nice around the... All good for your first flight. You've got this! With the Bluetooth backpacks in place, it's back up the barn's creaky ladder to take these baby owls back home. We just put them back so they are now in the corner sitting there quietly.

22:29They already closed their eyes. By tonight we should have their first locations. If we are successful in that, if we see that these tags are a good tool for barn owl tracking, then I would be really interested in to look more into the social structure of the population. How often do they meet out in the field when they are hunting or before they pair all these things that at the moment we cannot look at and all these research questions to answer is only possible because we have now this new technology and knowing a bird for so many years for such a long time and each year finding out some new things is amazing to me and it also makes me understand that the more I research the borne out the less I understand it.

23:20Scientists like Bettina are now using these trackers to study all kinds of species, from sloths to cockatoos. And it's all possible because Bluetooth devices are now so common, providing a huge network to pick up the signals from tags. But the sheer number of Bluetooth devices that surround us every day, from wireless keyboards to cars, from headphones to owl trackers, also has the potential to cause problems. Back in Cambridge with telecoms expert William, Rachel has one last question. Okay, so if you've got multiple different devices that are all operating within this same frequency band, how do they not get confused or mixed up between different devices?

24:01Yeah, so it's actually a real challenge. So the way that Bluetooth has overcome this is first of all to divide up this 2.4 gigahertz band into 80 tiny little subbands and each device when it transmits uses one of those 80 different subbands so that in principle allows lots of different devices to exist the problem is they're not coordinated so you might be using bluetooth with your phone and your headset and i might be in the same room using bluetooth with my phone and my headset and the two aren't talking to each other so it's not that one says to the other i know what you have channel six and I have channel eight they just don't do that and so you could well be in a situation where randomly two devices choose the same channel and then they would interfere with each other.

24:47But that doesn't happen despite there being only 80 Bluetooth bands and potentially hundreds of devices in range of each other just waiting to collide and that's down to a really clever solution. So what Bluetooth did to overcome that was it adopted something called frequency hopping and what that means is that it transmits for for quite a short period of time let's say a millisecond a thousandth of a second on one of those channels say channel one and then it will jump to a different one say channel 10 and then it will jump to another one channel 20 and each different bluetooth device is given a different what's called hopping sequence so there is a chance that at any point in time the two will end up on the same channel and they'll interfere but for the most part they won't if there's only two devices and there's 80 channels and they're both kind of fairly randomly hopping between them.

25:35And only one time in 80 will they end up on the same one. And the system is designed that if that happens, effectively you can overcome it using sort of an error correction system. So actually frequency hopping is the way that they avoid interfering with each other as long as there aren't too many of them. Okay, so if you've got my phone connected to my Bluetooth headphones, my phone is sending out a radio signal jumping around sort of seemingly randomly how do my headphones know where to look for the signal how do they know to go band 8 band 12 band 71 yeah so what actually happens in bluetooth is if those 80 channels typically three are reserved for the initial contact and in that initial contact the two devices will agree on the frequency hopping pattern they're going to use.

26:26In fact, the phone will say to the device, right, we're going to go for pattern 6382, and they both know what that pattern is, and then off they go. And essentially, they're able to then maintain contact through that pattern into the future. So Rachel's headphones start by listening on one of three special channels where Bluetooth devices announce their presence. Once her headphones and phone find each other, they agree on a carefully choreographed routine, hopping between frequencies 1 ,600 times every second, which means the air around you can be full of Bluetooth signals, seamlessly dancing around each other.

27:06That's almost all we have time for, but first let's check back in with Rachel. Rachel, how are you feeling? Do you feel like you understand how Bluetooth works now? Yeah, I think you've built such a great picture of the history of Bluetooth, how it works. I never would have guessed that it was radio waves that were behind the signals. Do you think when you next cycle along using your Bluetooth headphones? Exactly. I'm going to be picturing the radio waves coming out of my phone, hopping towards my headphones, yes. Thank you so much for getting in touch with your question, Rachel. There's a lot more to Bluetooth than I was expecting.

27:37From an experiment in an overlooked corner of the radio spectrum to connecting billions of devices worldwide, Bluetooth has come a long way. Today, it can do everything from tracking baby owls to helping you listen to CrowdScience. And finally, over to Rachel for the credits. That's it for this edition of CrowdScience from the BBC World Service. The presenter was Caroline Steele and the producer was Anand Jagatir. This week's question was for me, Rachel, in the UK. If you have a question that you'd like the team to investigate, email it to crowdscience at bbc.co.uk. Thank you for listening. And don't forget, you can also send your questions to us on WhatsApp.

28:18Just message us or send a voice note to plus 44 8000 314 773. That's plus 44 8000 314 773.

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