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<html devsite>
<head>
<title>Bluetooth Low Energy</title>
<meta name="project_path" value="/_project.yaml" />
<meta name="book_path" value="/_book.yaml" />
</head>
<body>
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<p>
Bluetooth Low Energy (BLE), available in Android 4.3 and later, creates
short connections between devices to transfer bursts of data. BLE
remains in sleep mode when not connected. This lets BLE provide lower
bandwidth and reduced power consumption compared to Classic Bluetooth.
It is ideal for applications such as a heart-rate monitor or a wireless
keyboard. To use BLE, devices need to have a chipset that supports BLE.
</p>
<h2 id="implementation">Implementation</h2>
<p>
All current BLE application profiles are based on the
<a href="https://www.bluetooth.com/specifications/gatt">Generic
Attribute Profile</a> (GATT). When an Android device interacts with a
BLE device, the device that sends information is the server and the
device that receives information is the client. Android includes
<a href="https://developer.android.com/guide/topics/connectivity/bluetooth-le.html">
developer APIs for BLE</a>, including APIs for interactions between
GATT servers and GATT clients. To fully leverage the BLE APIs,
implement the
<a href="/devices/bluetooth/hci_requirements.html">
Android Bluetooth HCI Requirements</a>.
</p>
<h2 id="device-modes">Device modes</h2>
<p>
When using BLE, an Android device can act as a peripheral device, a
central device, or both. Peripheral mode lets devices send
advertisement packets. Central mode lets devices scan for
advertisements. An Android device acting as both a peripheral and
central device can communicate with other BLE peripheral devices while
sending advertisements in peripheral mode. Devices supporting
Bluetooth 4.1 and earlier can only use BLE in central mode. Older
device chipsets may not support BLE peripheral mode.
</p>
<h2 id="ble-scanning">BLE scanning</h2>
<p>
An Android device can target and scan for specific Bluetooth devices
more efficiently when using BLE. BLE APIs let app developers create
filters for finding devices with less involvement from the host
controller.
</p>
<aside class="caution">
<strong>Caution:</strong> BLE scanning needs location permissions as BLE
scanning identifies objects that could be used for geolocation. Turning
off Location services will turn off Bluetooth scanning.
</aside>
<h3 id="location-scanning">Location scanning</h3>
<p>
A device's location services can use Bluetooth to detect Bluetooth
beacons and provide a more accurate location. This is how users
enable the feature:
</p>
<ol>
<li>Go to <strong>Settings</strong> > <strong> Security &
Location</strong> > <strong>Location</strong>.</li>
<li>Check that the Location <strong>On</strong>/<strong>Off</strong>
toggle is in the <strong>On</strong> position.</li>
<li>Go to <strong>Mode</strong>.</li>
<li>Select either <strong>High accuracy</strong> or <strong>Battery
saving</strong> mode.</li>
</ol>
<p>
Individual apps need location permissions to use BLE scanning, even
if they are scanning only to find devices to connect to. If the user
disables location scanning, or does not give an app location
permissions, then the app will not receive any BLE scanning results.
</p>
<p>
Users can disable system-level Bluetooth background scanning by
going to <strong>Settings</strong> > <strong>Security &
Location</strong> > <strong>Location</strong> > <strong>
Scanning</strong> and disabling the toggle for <strong>Bluetooth
scanning</strong>. This does not affect BLE scanning for location or
local devices.
</p>
<h3 id="filtering-scan-results">Filtering scan results</h3>
<p>
Android 6.0 and later includes BLE scanning and filter-matching on
the Bluetooth controller. A device can filter scan results and
report <strong>found</strong> and <strong>lost</strong> events
related to BLE devices to the application processor (AP). Filtering
also works for batch scans, which helps save power as BLE scanning is
offloaded to the firmware. Batch scans reduce how often the AP wakes
up due to BLE scanning for devices or beacons.
</p>
<p>
The <code>OnFound</code>/<code>OnLost</code> feature is implemented
in the Bluetooth controller and then tested to confirm that BLE
devices are not missed in scans. This provides power savings, and it
can also provide the following benefits:
</p>
<ul>
<li>For an <code>OnFound</code> event, the main AP wakes up upon the
discovery of a specific device.</li>
<li>For an <code>OnLost</code> event, the AP wakes up when a
specific device cannot be found.</li>
<li>Framework apps get fewer unwanted notifications when a nearby device is in range.</li>
<li>Continuous scans enable framework apps to be notified when a device is out of range.</li>
</ul>
<p>
A scan filter can be based on the discovery of a device's
advertisements (the <code>OnFound</code> event). The Java layer can
specify parameters such as first discovery (or a specified number of
advertisements since first discovery). Implement BLE filtering using
the <a href="/devices/bluetooth/hci_requirements#advertisement-packet-content-filter">
Advertising Packet Content Filter HCI command</a>.
</p>
</body>
</html>
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