You are here: Home page > Communications > Bluetooth

A pair of USB Bluetooth adapters/dongles photographed against a black computer keyboard.


Is there anything worse than wires? If you've ever hooked up a computer and half a dozen peripherals (add-ons), a digital television and a DVD player, or run your own telephone extensions through the house, you'll know just what a pain all those cables can be. Wouldn't it be nice if there were a way of bringing electronic gadgets together so they could share whatever signals they need without any wires at all? Enter Bluetooth! It's a simple way for cellphones, printers, PCs, digital cameras, and other gadgets to link together over relatively short distances using wireless (radio wave) technology. The curious name comes from Harald Bluetooth, a Danish king who united the Scandinavians in the 10th century. Will Bluetooth unite the electronic world the same way? Let's take a closer look!

Photo: Almost all new laptops and cellphones have Bluetooth built in. For older laptops and desktop computers without the feature, you can generally add Bluetooth by plugging in a small USB adapter, like these.

Sponsored links


  1. What is Bluetooth?
  2. How does Bluetooth work?
  3. What is spread spectrum?
  4. Is Bluetooth secure?
  5. Is Bluetooth better or worse than Wi-Fi?
  6. How is Bluetooth evolving?
  7. Find out more

What is Bluetooth?

We're all use to wireless communication by now, even if we don't always realize it. Radio receivers and television sets pick up programs beamed in radio waves hundreds (possibly even thousands) of km/miles through the air. Cordless telephones use similar technologies to carry calls from a handset to a base station somewhere in your home. If you use Wi-Fi (wireless Internet), your computer sends and receives a steady stream of Internet data to and from a router that's probably wired directly to the Net. All these technologies involve sending information back and forth not along copper cables but in radio waves buzzing invisibly through the air.

Using Bluetooth to connect a full-sized keyboard to an Android smartphone.

Photo: A typical use of Bluetooth: connecting a full-sized keyboard to a tablet or smartphone. Wireless connections like this are particularly useful when you're using portable gadgets, maybe on a train or a plane, and cables would really get in the way.

Bluetooth is a similar radio-wave technology, but it's mainly designed for communicating over short distances less than about 10m or 30ft. [1] Typically, you might use it to download photos from a digital camera to a PC, to hook up a wireless mouse to a laptop, to link a hands-free headset to your cellphone so you can talk and drive safely at the same time, and so on. Electronic gadgets that work this way have built-in radio antennas (transmitters and receivers) so they can simultaneously send and receive wireless signals to other Bluetooth gadgets. Older gadgets can be converted to work with Bluetooth using plug-in adapters (in the form of USB sticks, PCMCIA laptop cards, and so on). The power of the transmitter governs the range over which a Bluetooth device can operate and, generally, devices are said to fall into one of three classes: class 1 are the most powerful and can operate up to 100m (330ft), class 2 (the most common kind) operate up to 10m (33ft), and class 3 are the least powerful and don't go much beyond 1m (3.3ft). [2]

Sponsored links

How does Bluetooth work?

Bluetooth sends and receives radio waves in a band of 79 different frequencies (channels) centered on 2.45 GHz, set apart from radio, television, and cellphones, and reserved for use by industrial, scientific, and medical gadgets. [3] Don't worry: you're not going to interfere with someone's life-support machine by using Bluetooth in your home, because the low power of your transmitters won't carry your signals that far! Bluetooth's short-range transmitters are one of its biggest plus points. They use virtually no power and, because they don't travel far, are theoretically more secure than wireless networks that operate over longer ranges, such as Wi-Fi. (In practice, there are some security concerns.)

Two nearby Bluetooth devices exchange a pairing request.

Photo: Connecting with Bluetooth is simplicity itself. Simply enable Bluetooth on both devices, put them reasonably near one another, and they'll recognize one another and make a "pairing request." Select "pair" on each device and they connect. The devices can be completely different things: here I'm pairing an LG smartphone (left) with an Apple iPod Touch (right).

Bluetooth devices automatically detect and connect to one another and up to eight of them can communicate at any one time. They don't interfere with one another because each pair of devices uses a different one of the 79 available channels. If two devices want to talk, they pick a channel randomly and, if that's already taken, randomly switch to one of the others (a technique known as spread-spectrum frequency hopping). To minimize the risks of interference from other electrical appliances (and also to improve security), pairs of devices constantly shift the frequency they're using—thousands of times a second.

When a group of two or more Bluetooth devices are sharing information together, they form a kind of ad-hoc, mini computer network called a piconet. Other devices can join or leave an existing piconet at any time. One device (known as the master) acts as the overall controller of the network, while the others (known as slaves) obey its instructions. Two or more separate piconets can also join up and share information forming what's called a scatternet.

A smartphone links to a pulse oximeter and a blood-pressure monitor using Bluetooth

Photo: Monitoring a patient's health with Bluetooth®: the smartphone is taking readings from the blood-pressure monitor and pulse oximeter (finger-mounted oxygen monitor). Photo by Patricia Deal courtesy of US Army and DVIDS.

What is spread spectrum?

A torpedo fires from the deck of a warship

Photo: Spread-spectrum was designed for use in wartime to stop jamming of radio signals between warships and the torpedoes they fired. Photo by John L. Beeman courtesy of US Navy and Wikimedia Commons.

Suppose you're talking to a friend on a walkie-talkie or with a CB (citizen's band) radio, but there are other people using the same frequency and your conversation keeps getting interrupted. What can you do? Most experienced radio users know the answer: you both change to a different frequency (band) and resume your conversation there. And you can keep on switching band until you find a place where you can happily talk without interruption. In theory, you could use the same technique for covert communication: if you were talking over the radio and someone was eavesdropping, you could give a code-word to your friend and hastily switch to another, pre-arranged frequency band where the eavesdropper wouldn't find you (although they'd most likely still pick up your signal sooner or later).

Radios are clever electronic gadgets, so why can't they do this neat trick for themselves? Why can't they simply switch to another frequency automatically to prevent interference and eavesdropping? This is the basic idea behind a technique called spread-spectrum frequency hopping, where signals are rapidly and randomly switched across a wide range of different frequencies to improve the security and reliability of wireless communication.

Who invented it?

Numerous inventors contributed to the invention of spread-spectrum, including electricity pioneer Nikola Tesla (1856–1943) and US actress Hedy Lamarr (1913–2000), who, with the help of George Antheil, developed a practical system for the US military during World War II. While modern spread-spectrum systems are electronically controlled, Lamarr's, which is illustrated below, was based on the mechanical, punched paper-tape technology originally used in player pianos. The sender and receiver each had identical machines with precisely synchronized electric motors that slowly pulled lengths of paper tape through them. The two tapes were punched with matching patterns of holes indicating which of 88 different radio frequencies the sender and receiver should use to communicate with each other at any particular time. As the tape chugged through the machines, communication switched from one frequency to another, in tandem, in a way that was completely unpredictable to outside observers. Since the radio transmissions were often extremely brief signals for steering torpedoes, it was quite likely that an enemy wouldn't pick them up at all or know what they meant even if they did.

Illustration of secret spread-spectrum communication from Hedy Lamarr's US Patent 2,292,387

Artwork: Secret, spread-spectrum communication, as envisaged by Hedy Lamarr. I've colored and simplified it to make it easier to follow. A length of paper tape (blue) is punched with holes that encode a secret list of frequencies. A machine like a player-piano detector (red) reads the pattern of holes and sends corresponding electrical signals to a radio tuning system (green) that picks one of 88 possible frequencies on which to beam signals out to the receiver using a standard radio transmitter (orange). The receiver has similar equipment and switches to the same frequency at the same time. Artwork from US Patent 2,292,387: Secret communication system courtesy of US Patent and Trademark Office.

Further reading

Is Bluetooth secure?

Wireless is always less secure than wired communication. Remember how old spy films used to show secret agents tapping into telephone wires to overhear people's conversations? Cracking wired communication is relatively difficult. Eavesdropping on wireless is obviously much easier because information is zapping back and forth through the open air. All you have to do is be in range of a wireless transmitter to pick up its signals. Wireless Internet networks are encrypted (use scrambled communications) to get around this problem.

How secure is Bluetooth? Like Wi-Fi, communications are encrypted too and there are numerous other security features. You can restrict certain devices so they can talk only to certain other, trusted devices—for example, allowing your cellphone to be operated only by your Bluetooth hands-free headset and no-one else's. This is called device-level security. You can also restrict the things that different Bluetooth gadgets can do with other devices using what's called service-level security.

Criminals get more sophisticated all the time; you've probably heard about bluebugging (people taking over your Bluetooth device without your knowledge), bluejacking (where people send messages to other people's devices, often for advertising purposes), and bluesnarfing (downloading information from someone else's device using a Bluetooth connection) and doubtless there are more ways of hacking into Bluetooth networks still to come. Generally, though, providing you take reasonable and sensible precautions if you use Bluetooth devices in public places, security shouldn't worry you too much.

Connecting a wireless phone to a wireless speaker with Bluetooth

Photo: Connecting a wireless phone to a wireless speaker with Bluetooth.

Is Bluetooth better or worse than Wi-Fi?

People often get confused by Bluetooth and Wi-Fi because, at first sight, they seem to do similar things. In fact, they're very different. Bluetooth is mainly used for linking computers and electronic devices in an ad-hoc way over very short distances, often for only brief or occasional communication using relatively small amounts of data. It's relatively secure, uses little power, and connects automatically. Wi-Fi is designed to shuttle much larger amounts of data between computers and the Internet, often over much greater distances. It can involve more elaborate security and it generally uses much higher power. Bluetooth and Wi-Fi are complementary technologies, not rivals, and you can easily use both together to make your electronic gadgets work more conveniently for you!

Marley Simmer Down Bluetooth louspeakers

Photo: Look no wires: A pair of Marley Bluetooth loudspeakers. One of them is battery powered, for perfect portability—or you can use them together on AC power.

How is Bluetooth evolving?

Bluetooth has often been quite tricky to use: like any wireless technology, it's another battery drainer for mobile devices; you can often step out of range, making communication erratic or impossible; and even getting two Bluetooth devices to talk to one another in the first place isn't always as simple as it should be. The world of mobile devices is changing as we move toward the so-called Internet of Things (where all kinds of everyday objects become net-connected)—and Bluetooth has to keep evolving to keep up.

Simple line artwork showing how Bluetooth links a laptop, a wireless mouse, headphones, and a tablet.

Recognizing the need to connect an increasing range of devices, more quickly, and more securely, Bluetooth's developers are regularly coming up with improved versions. First, there was Bluetooth BR/EDR (Basic Rate/Enhanced Data Rate, technically Bluetooth Version 2.1), offering simpler connectivity between devices and better security. Next came Bluetooth Highspeed (Bluetooth Version 3.0), which offered faster communication and lower power consumption. More recently, we've had Bluetooth Smart or Bluetooth Low Energy (technically referred to as Bluetooth Version 4.0+); As these names suggest, this version is better at connecting a wider range of simpler devices, uses much less power, and is much easier to integrate into mobile (iOS and Android) applications. The latest version, Bluetooth 5, offers another boost in speed, range, and bandwidth. Another innovation called Auracast™ (formerly "Bluetooth Audio Sharing") makes it possible for one audio device (such as a smartphone) to power unlimited other devices (multiple sets of headphones or hearing aids, for example).

Sponsored links

Find out more

On this website

On other websites




  1.    Technically, it is possible to use Bluetooth over much longer distances than this. See for example this article from IEEE Spectrum, which describes how Bluetooth can be used at distances of over 30km (20 miles) for asset tracking applications.
  2.    Ranges documented in Section " Bluetooth" of Mobile Peer to Peer (P2P): A Tutorial Guide by Frank H. P. Fitzek, Hassan Charaf, Wiley, 2009, p.7.
  3.    For more details of the 79 carrier frequencies and how the frequency hopping works, see p.162 of Emerging Wireless LANs, Wireless PANs, and Wireless MANs by Yi Pan, Yang Xiao, Wiley, 2009.

Please do NOT copy our articles onto blogs and other websites

Articles from this website are registered at the US Copyright Office. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties.

Text copyright © Chris Woodford 2009, 2023. All rights reserved. Full copyright notice and terms of use.

Bluetooth and Auracast are registered trademarks owned by Bluetooth SIG, Inc.

Follow us

Rate this page

Please rate or give feedback on this page and I will make a donation to WaterAid.

Tell your friends

If you've enjoyed this website, please kindly tell your friends about us on your favorite social sites.

Press CTRL + D to bookmark this page for later, or email the link to a friend.

Cite this page

Woodford, Chris. (2009/2023) Bluetooth. Retrieved from [Accessed (Insert date here)]


@misc{woodford_bluetooth, author = "Woodford, Chris", title = "Bluetooth", publisher = "Explain that Stuff", year = "2009", url = "", urldate = "2023-03-31" }

More to explore on our website...

Back to top