ExplainerBluetooth

How Bluetooth pairing works

Learn what happens when two Bluetooth devices pair, why pairing mode exists, and what the codes and prompts mean, in plain words.

  • Updated
  • 6 min
  • Beginner
Applies to
  • Any device

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Pairing is a one-time introduction between two Bluetooth devices, such as a phone and a pair of headphones. Learn what happens during pairing, why a device needs "pairing mode", and what the codes and prompts mean.

The core idea: pair once, connect many times

Bluetooth is a short-range radio link between two devices. Before two devices can trust each other, they need an introduction. That introduction is pairing. During pairing, the two devices create a secret key that only they share, and each one saves it.

After that, the devices use the saved key to recognize each other. This is why headphones you paired last week usually connect on their own when you switch them on. Pairing happens once. Connecting happens every time you use the devices.

The five stages of Bluetooth pairing5 numbered steps, one under the other. The full text follows the picture.The five stages of Bluetoothpairing1Pairing modeThe accessory announcesthat it is ready to be found2SearchYour phone or computer liststhe Bluetooth devices nearby3ConfirmYou tap Pair, compare acode, or type a code4Save the keyBoth devices store a secretkey that only they share5ReconnectNext time they connect ontheir own when both are onand close
You repeat the first four stages only if one device forgets the other.
Text version of this diagram
  1. Pairing mode: The accessory announces that it is ready to be found
  2. Search: Your phone or computer lists the Bluetooth devices nearby
  3. Confirm: You tap Pair, compare a code, or type a code
  4. Save the key: Both devices store a secret key that only they share
  5. Reconnect: Next time they connect on their own when both are on and close

Why a device must be in pairing mode

Most Bluetooth devices stay hidden, so strangers nearby cannot see them or try to connect. Pairing mode, also called discoverable mode, makes a device visible for a short time. Many accessories have a pairing button, or you hold the power button until a light starts to blink. The accessory's manual shows how. The US standards body NIST advises that a device should be discoverable only for the minimal time needed to pair.

Two devices about to pairA phone on the left and a speaker on the right with a Bluetooth symbol and radio waves between them. The speaker has a small pairing button on top. It has 4 numbered markers, explained in the list under the picture.1234Two devices about to pair
  1. Your phone or computer: it searches for nearby devices
  2. The accessory: it must be in pairing mode to be found
  3. Pairing button: hold it until the light blinks
  4. Radio link: short range, so keep both close
Button names and positions differ between accessories.
Text version of this diagram

A phone on the left and a speaker on the right with a Bluetooth symbol and radio waves between them. The speaker has a small pairing button on top.

  1. Your phone or computer: it searches for nearby devices
  2. The accessory: it must be in pairing mode to be found
  3. Pairing button: hold it until the light blinks
  4. Radio link: short range, so keep both close

Start the search on your phone or computer right after you put the accessory in pairing mode. An accessory that is already connected to another device may not show up for a new one. Turn Bluetooth off on the other device, or remove the accessory there, then try again.

How the devices check they have the right partner

Pairing also includes a check that you are linking the right two devices. Which check you see depends on what each device can show or accept.

Common ways Bluetooth devices confirm a pairing
What you seeWhat it is calledWhere you meet it
Nothing, or only a Pair buttonNo-confirmation pairingDevices with no screen or keypad, such as headsets
The same 6-digit number on both screensNumeric comparisonTwo devices that both have screens
A 6-digit number on one screen, to type on the otherPasskey entryA keyboard paired with a phone or computer
Touching the two devices togetherOut of band (NFC tap)Devices that support NFC
A PIN to type on one or both devicesPIN pairingOlder devices, from before Bluetooth 2.1

With a code, you confirm that you have the right device. Someone who sees the code cannot use it to work out the secret key. With no-confirmation pairing there is no code to compare, so you cannot tell if a different device answered. That is why you should pair in a place you trust, such as at home.

Bluetooth and Wi-Fi are different tools

Bluetooth links two devices directly over a short distance. Wi-Fi connects your devices to the internet through a router. Many phones and accessories are designed to work up to about 33 feet (10 meters) away in open space, and walls or your body can shorten that. Both can use the 2.4 GHz radio band, so a busy network there can sometimes disturb Bluetooth. See Wi-Fi bands explained.

Bluetooth and Wi-Fi at a glance2 options compared on 2 measures, each scored from 1 to 5. The full text follows the picture.Bluetooth and Wi-Fi at a glanceBluetoothHeadphones, keyboards, car callsRange2 of 5Speed1 of 5Wi-FiInternet, video, large filesRange4 of 5Speed5 of 5
A rough, relative comparison for everyday devices. Real results vary.
Text version of this diagram
  • Bluetooth: Range 2 out of 5, Speed 1 out of 5. Headphones, keyboards, car calls.
  • Wi-Fi: Range 4 out of 5, Speed 5 out of 5. Internet, video, large files.

What this means for you

  • Put the accessory in pairing mode first, then search on your phone or computer straight away.
  • Keep both devices close, within a few feet, while you pair.
  • Pair once. After that, switching the accessory on should be enough. If it does not connect, see Bluetooth won't pair or connect.
  • If a device that used to work stops connecting, remove ("forget") it on both devices, then pair again. This creates a new secret key.
  • Remove devices you no longer use. A paired device is trusted by the other, and you can always pair it again later.

Accept only pairing requests you started

If your phone or computer asks you to pair, or shows a code, and you did not start a pairing, decline it. Pair only with devices you recognize, at home or in another place you trust.

Ready to pair? See the steps for Windows, Mac, or Android and iPhone.

Frequently asked questions

Do I have to pair every time I use a device?

No. Pair once. After that, the devices reconnect on their own when both are switched on, Bluetooth is on, and they are close together.

Why can't I find my headphones in the list?

They may not be in pairing mode, they may be too far away, or they may be connected to another device. Put them in pairing mode again, move them closer, and turn Bluetooth off on the other device.

Does Bluetooth use my Wi-Fi or mobile data?

No. Bluetooth links two devices directly. Some apps that control a Bluetooth device may use the internet for other things.

Why does an older accessory ask for a PIN?

Older Bluetooth devices, from before version 2.1, pair with a PIN that you type on one or both devices. The accessory's manual lists the PIN.

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Pages consulted while preparing this guide. Check them for the latest details.

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