Find Bluetooth devices
Using the BluetoothAdapter , you can find remote Bluetooth devices either through device discovery or by querying the list of paired devices.
Make sure you have the appropriate Bluetooth permissions and set up your app for Bluetooth before attempting to find Bluetooth devices.
Device discovery is a scanning procedure that searches the local area for Bluetooth-enabled devices and requests some information about each one. This process is sometimes referred to as discovering, inquiring, or scanning. A nearby Bluetooth device responds to a discovery request only if it is currently accepting information requests by being discoverable. If a device is discoverable, it responds to the discovery request by sharing some information, such as the device’s name, its class, and its unique MAC address. Using this information, the device that is performing the discovery process can then choose to initiate a connection to the discovered device.
Because discoverable devices might reveal information about the user’s location, the device discovery process requires location access. If your app is being used on a device that runs Android 8.0 (API level 26) or higher, consider using the Companion Device Manager API instead. This API performs device discovery on your app’s behalf, so your app doesn’t need to request location permissions.
Once a connection is made with a remote device for the first time, a pairing request is automatically presented to the user. When a device is paired, the basic information about that device—such as the device’s name, class, and MAC address—is saved and can be read using the Bluetooth APIs. Using the known MAC address for a remote device, a connection can be initiated with it at any time without performing discovery, assuming the device is still within range.
Note that there is a difference between being paired and being connected:
- To be paired means that two devices are aware of each other’s existence, have a shared link-key that can be used for authentication, and are capable of establishing an encrypted connection with each other.
- To be connected means that the devices currently share an RFCOMM channel and are able to transmit data with each other. The current Bluetooth APIs require devices to be paired before an RFCOMM connection can be established. Pairing is automatically performed when you initiate an encrypted connection with the Bluetooth APIs.
The following sections describe how to find devices that have been paired and how to discover new devices using device discovery.
Note: Android-powered devices are not discoverable by default. A user can make the device discoverable for a limited time through the system settings, or an app can request that the user enable discoverability without leaving the app. For more information, see the enable discoverability section on this page.
Query paired devices
Before performing device discovery, it’s worth querying the set of paired devices to see if the desired device is already known. To do so, call getBondedDevices() . This returns a set of BluetoothDevice objects representing paired devices. For example, you can query all paired devices and get the name and MAC address of each device, as the following code snippet demonstrates:
Kotlin
val pairedDevices: Set? = bluetoothAdapter?.bondedDevices pairedDevices?.forEach < device ->val deviceName = device.name val deviceHardwareAddress = device.address // MAC address >
Java
Set pairedDevices = bluetoothAdapter.getBondedDevices(); if (pairedDevices.size() > 0) < // There are paired devices. Get the name and address of each paired device. for (BluetoothDevice device : pairedDevices) < String deviceName = device.getName(); String deviceHardwareAddress = device.getAddress(); // MAC address >>
To initiate a connection with a Bluetooth device, all that’s needed from the associated BluetoothDevice object is the MAC address, which you retrieve by calling getAddress() . You can learn more about creating a connection in Connect Bluetooth devices.
Discover devices
To start discovering devices, call startDiscovery() . The process is asynchronous and returns a boolean value indicating whether discovery has successfully started. The discovery process usually involves an inquiry scan of about 12 seconds, followed by a page scan of each device found to retrieve its Bluetooth name.
To receive information about each device discovered, your app must register a BroadcastReceiver for the ACTION_FOUND intent. The system broadcasts this intent for each device. The intent contains the extra fields EXTRA_DEVICE and EXTRA_CLASS , which in turn contain a BluetoothDevice and a BluetoothClass , respectively. The following code snippet shows how you can register to handle the broadcast when devices are discovered:
Kotlin
override fun onCreate(savedInstanceState: Bundle?) < . // Register for broadcasts when a device is discovered. val filter = IntentFilter(BluetoothDevice.ACTION_FOUND) registerReceiver(receiver, filter) >// Create a BroadcastReceiver for ACTION_FOUND. private val receiver = object : BroadcastReceiver() < override fun onReceive(context: Context, intent: Intent) < val action: String = intent.action when(action) < BluetoothDevice.ACTION_FOUND -> < // Discovery has found a device. Get the BluetoothDevice // object and its info from the Intent. val device: BluetoothDevice = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE) val deviceName = device.name val deviceHardwareAddress = device.address // MAC address >> > > override fun onDestroy() < super.onDestroy() . // Don't forget to unregister the ACTION_FOUND receiver. unregisterReceiver(receiver) >
Java
@Override protected void onCreate(Bundle savedInstanceState) < . // Register for broadcasts when a device is discovered. IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND); registerReceiver(receiver, filter); >// Create a BroadcastReceiver for ACTION_FOUND. private final BroadcastReceiver receiver = new BroadcastReceiver() < public void onReceive(Context context, Intent intent) < String action = intent.getAction(); if (BluetoothDevice.ACTION_FOUND.equals(action)) < // Discovery has found a device. Get the BluetoothDevice // object and its info from the Intent. BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE); String deviceName = device.getName(); String deviceHardwareAddress = device.getAddress(); // MAC address >> >; @Override protected void onDestroy() < super.onDestroy(); . // Don't forget to unregister the ACTION_FOUND receiver. unregisterReceiver(receiver); >
To initiate a connection with a Bluetooth device, you call getAddress() on the BluetoothDevice to retrieve the associated MAC address.
Caution: Performing device discovery consumes a lot of the Bluetooth adapter’s resources. After you have found a device to connect to, be certain that you stop discovery with cancelDiscovery() before attempting a connection. Also, you shouldn’t perform discovery while connected to a device because the discovery process significantly reduces the bandwidth available for any existing connections.
Enable discoverability
To make the local device discoverable to other devices, call startActivityForResult(Intent, int) with the ACTION_REQUEST_DISCOVERABLE intent. This issues a request to enable the system’s discoverable mode without having to navigate to the Settings app, which would stop your own app. By default, the device becomes discoverable for two minutes. You can define a different duration, up to one hour, by adding the EXTRA_DISCOVERABLE_DURATION extra.
Caution: If you set the EXTRA_DISCOVERABLE_DURATION extra’s value to 0, the device is always discoverable. This configuration is insecure and therefore highly discouraged.
The following code snippet sets the device to be discoverable for five minutes:
Kotlin
val requestCode = 1; val discoverableIntent: Intent = Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE).apply < putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300) >startActivityForResult(discoverableIntent, requestCode)
Java
int requestCode = 1; Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE); discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300); startActivityForResult(discoverableIntent, requestCode);
Figure 2: The enabling discoverability dialog.
A dialog is displayed, requesting the user’s permission to make the device discoverable, as shown in figure 2. If the user responds «Allow,» then the device becomes discoverable for the specified amount of time. Your activity then receives a call to the onActivityResult() callback, with the result code equal to the duration that the device is discoverable. If the user responded «Deny», or if an error occurred, the result code is RESULT_CANCELED .
Note: If Bluetooth has not been enabled on the device, then making the device discoverable automatically enables Bluetooth.
The device silently remains in discoverable mode for the allotted time. To be notified when the discoverable mode has changed, register a BroadcastReceiver for the ACTION_SCAN_MODE_CHANGED intent. This intent contains the extra fields EXTRA_SCAN_MODE and EXTRA_PREVIOUS_SCAN_MODE , which provide the new and old scan mode, respectively. Possible values for each extra are as follows:
SCAN_MODE_CONNECTABLE_DISCOVERABLE The device is in discoverable mode. SCAN_MODE_CONNECTABLE The device isn’t in discoverable mode but can still receive connections. SCAN_MODE_NONE The device isn’t in discoverable mode and cannot receive connections.
If you are initiating the connection to a remote device, you don’t need to enable device discoverability. Enabling discoverability is only necessary when you want your app to host a server socket that accepts incoming connections, as remote devices must be able to discover other devices before initiating connections to those other devices.
Content and code samples on this page are subject to the licenses described in the Content License. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
Last updated 2021-10-27 UTC.
Pairing Bluetooth mobile devices in 3 steps
Nowadays this wireless technology is a common standard that allows us to connect different types of units without any cables or cords. What is Bluetooth used for? It may be used to join a mobile to a car, to join headset to our phone, to use wireless keyboard and mouse with tablet or phone, to act our phone as a modem, to connect mobile to mobile, etc. The average working distance for this technology is not more than about 10 meters so we shouldn’t move connected ones too far from each other.
Today the mobiles are very popular. The total count of them is more that people in the world. So we should know how to connect Bluetooth to the phone to stay modern.
The second device type is varied. One of the most popular wireless gadgets for mobile is a headset. Here is a manual on how to connect the Bluetooth headset unit in 4 steps. Another popular option is pairing a phone with car.
The generic main steps are
We don’t need to connect the units again in further. They automatically connect when they are in the range of each other with wireless mode turned on. Note that using modern technology can increase the level of battery utilization, so we should check the charge level on both units regularly.
Turn off the wireless mode just in case of stop usage. Remove each one from a paired list of other one to completely unpair Bluetooth devices if needed.
The most mobiles released after 2007 have this technology onboard. We may always check it through finding an appropriate setting on the one. Below are detailed pairing instructions for different types such as
How to connect Bluetooth on iPhone and iPad#
Ensure that wireless mode is on, do the same on the second unit and tap on its name in the list of available equipment. The user interface is quite the same for iPad by thanks to Apple.
Check Bluetooth passkey (or enter it if necessary) and choose “Pair” to accept the connection.
Now the mobile and the other unit are paired.
Open it details via information icon and choose “Forget this Device” to unpair the device if necessary.
Attach Bluetooth on Android phone and tablet#
Ensure that wireless technology is on in “Settings\Bluetooth” and tap on the particular available device that must be wirelessly activated too. Repeat search by “Search for devices” or similar if we can’t find a particular unit in the list.
Check passkey for Bluetooth (or enter it if necessary) and confirm the connection.
Open it details via configuration icon and choose “Unpair” to disconnect the unit. Also, we can set own local name of paired one via “Rename”.
How to connect Bluetooth on Windows Phone#
Make sure that the mode is on (look at the below picture) and get the list of available ones. The second one should be enabled too. Then find and tap on the second unit name.
Now the mobile and the other unit are paired.
Tap on device in the list and confirm deletion to unpair it in case of no need.