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<!DOCTYPE HTML>
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<title>Bluetooth Low Energy (BLE) identifier reference | diyActive</title>
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<meta name="description" content="A just-technical-enough overview of BLE device identification, including examples of device behaviour.">
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<h1>
Bluetooth Low Energy (BLE) Identifier Reference <br>
<small> Overview of BLE device identification </small>
</h1>
<p> At <a href="https://www.reelyactive.com" target="_blank">reelyActive</a>, we often get asked questions like <i>"how much can one know about a person's smartphone from its Bluetooth packets?"</i> or <i>"can I recognise subsequent visits of the same device?"</i> This is intended to be a just-technical-enough reference for anyone to not only find answers to such questions but, more importantly, to understand why. </p>
<p> The following is a primer on radio-frequency identification using BLE. Specifics on the identifiers can be found below. </p>.
<div class="embed-responsive embed-responsive-16by9">
<iframe src="//www.slideshare.net/slideshow/embed_code/key/8vIKvMlPpRIveE" width="595" height="485" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" style="border:1px solid #CCC; border-width:1px; margin-bottom:5px; max-width: 100%;" allowfullscreen> </iframe>
</div>
<h2> Mandatory identifier <br>
<small> What has 48-bits and comes in three flavours? </small> </h2>
<p> The <b>advertiser address</b> is the one and only mandatory identifier in a BLE advertising packet. It has the form <tt>12:34:56:78:9a:bc</tt>. </p>
<p> BLE includes a feature which allows this identifier to be either <b><i>public</i></b> (IEEE-assigned) or <b><i>random</i></b> (manufacturer-assigned). Moreover, when random, the device manufacturer is free to change the identifier dynamically, should they so choose. The result is the following three flavours: </p>
<ul>
<li>
<tt>public static</tt>
<ul>
<li> manufacturer selects unique identifier from a block of IEEE-assigned addresses </li>
<li> by definition, this identifier must remain static </li>
</ul>
</li>
<li>
<tt>random static</tt>
<ul>
<li> manufacturer assigns unique identifier at its discretion </li>
<li> manufacturer elects for this identifier to remain static </li>
</ul>
</li>
<li>
<tt>random dynamic</tt>
<ul>
<li> manufacturer assigns unique identifier at its discretion </li>
<li> manufacturer elects to change this identifier periodically </li>
</ul>
</li>
</ul>
<p> There <i>IS</i> a mandatory flag to indicate whether the address is public or random. However, there <i>IS NOT</i> a flag to indicate whether a random address is static or dynamic. In other words: </p>
<blockquote> the only way to know if a device's <i>random</i> advertiser address will periodically change is through observation </blockquote>
<table class="table table-striped table-reelyactive">
<caption> COMMON QUESTIONS ABOUT THE 48-BIT ADVERTISER ADDRESS </caption>
<thead>
<tr>
<th> Question </th>
<th> <tt>public static</tt> </th>
<th> <tt>random static</tt> </th>
<th> <tt>random dynamic</tt> </th>
</tr>
</thead>
<tbody>
<tr>
<td> Can I implicitly recognise the product? </td>
<td> No* </td>
<td> No </td>
<td> No </td>
</tr>
<tr>
<td> Can I explicitly associate with a person/product? </td>
<td> Yes </td>
<td> Yes </td>
<td> No </td>
</tr>
<tr>
<td> Can I recognise the device again if it leaves and comes back? </td>
<td> Yes </td>
<td> Yes </td>
<td> No </td>
</tr>
<tr>
<td> Is the identifier guaranteed to be unique? </td>
<td> Yes </td>
<td> No </td>
<td> No </td>
</tr>
</tbody>
</table>
<p class="text-right"> <i>*it is nonetheless possible to look up the chip manufacturer from <a href="https://regauth.standards.ieee.org/standards-ra-web/pub/view.html#registries" target="_blank">this registry</a>.</i> </p>
<h2> Optional identifiers <br>
<small> But wait, there may be more! </small> </h2>
<p> Beyond the mandatory identifier, the standard BLE advertising packet supports up to 31 bytes more payload which may contain additional identifiers. </p>
<h3> 16-bit UUID </h3>
<p> A <b>16-bit UUID</b> represents a defined service. It has the form <tt>0x1234</tt>. </p>
<p> The Bluetooth SIG has reserved a block of 512 such UUIDs for member companies, <a href="https://www.bluetooth.com/specifications/assigned-numbers/16-bit-uuids-for-members" target="_blank">listed here</a>. It is therefore possible to look up the member company from the UUID. reelyActive maintains this lookup feature in <a href="https://sniffypedia.org" target="_blank">Sniffypedia</a>. Notable examples include: </p>
<h4> Eddystone </h4>
<p> Google's <b>Eddystone</b> service uses the UUID <b><tt>0xfeaa</tt></b>. An open specification, Eddystone includes several flavours that are free for use. These include: </p>
<ul>
<li> <a href="https://github.com/google/eddystone/tree/master/eddystone-uid#eddystone-uid" target="_blank">Eddystone-UID</a> which encodes a 16-bit Beacon ID consisting of a 10-bit namespace and 6-bit instance </li>
<li> <a href="https://github.com/google/eddystone/tree/master/eddystone-eid#eddystone-eid" target="_blank">Eddystone-EID</a> which encodes an encrypted ephemeral 8-bit identifier that can only be resolved by the remote service with which it was registered </li>
<li> <a href="https://github.com/google/eddystone/tree/master/eddystone-url#eddystone-url" target="_blank">Eddystone-URL</a> which encodes a compressed URL (limited in length by the BLE payload capacity) </li>
</ul>
<h4> Tile </h4>
<p> Tile devices advertise the UUID <b><tt>0xfeed</tt></b>. </p>
<h4> Contact Tracing </h4>
<p> Devices implementing the Contact Tracing service, a collaboration between Apple and Google in response to the COVID-19 pandemic (<a href="https://www.apple.com/covid19/contacttracing/" target="_blank">specification</a>), advertise the UUID <b><tt>0xfd6f</tt></b>. </p>
<h3> 128-bit UUID </h3>
<p> A <b>128-bit UUID</b> represents a service and/or acts as a device identifier. It has the form <tt>12345678-1234-1234-1234-123456789abc</tt>. Unlike the 16-bit UUID and the 16-bit company identifier used in Manufacturer Specific Data, the Bluetooth SIG does not assign 128-bit UUIDs, leaving vendors and programmers free to choose. Notable examples include: </p>
<h4> Fitbit </h4>
<p> Fitbit devices advertise the UUID <b><tt>adabXXXX-6e7d-4601-bda2-bffaa68956ba</tt></b> where the XXXX represents a specific product type such as the Charge HR. </p>
<h3> Manufacturer Specific Data </h3>
<p> Manufacturer Specific Data is accompanied by a <b>16-bit company identifier</b>. It has the form <tt>0x1234</tt>. </p>
<p> The Bluetooth SIG assigns the company identifiers which are <a href="https://www.bluetooth.com/specifications/assigned-numbers/company-identifiers" target="_blank">listed here</a>. It is therefore possible to look up the member company from the company identifier. reelyActive maintains this lookup feature in <a href="https://sniffypedia.org" target="_blank">Sniffypedia</a>. Notable examples include: </p>
<h4> iBeacon </h4>
<p> <b>Apple</b> is assigned the company code <b><tt>0x004c</tt></b> and their devices make extensive use of Manufacturer Specific Data for a variety of functions. While Apple does not openly document most of these functions, <a href="https://developer.apple.com/ibeacon/" target="_blank">the iBeacon specification</a> is a notable exception. </p>
<p> An iBeacon encodes a 128-bit UUID, a 16-bit Major and a 16-bit Minor identifier. Typically, the Major represents a superclass (ex: a physical venue) and the Minor represents a subclass (ex: points of interest within the venue), while the UUID is unique to a beacon vendor or operator, for example: </p>
<table class="table table-striped table-reelyactive">
<caption> COMMON IBEACON UUIDS AND THEIR ASSOCIATED VENDORS </caption>
<thead>
<tr>
<th> iBeacon UUID </th>
<th> Vendor </th>
</tr>
</thead>
<tbody>
<tr>
<td> <tt> f7826da6-4fa2-4e98-8024-bc5b71e0893e </tt> </td>
<td> Kontakt.io </td>
</tr>
<tr>
<td> <tt> 2f234454-cf6d-4a0f-adf2-f4911ba9ffa6 </tt> </td>
<td> Radius Networks </td>
</tr>
<tr>
<td> <tt> b9407f30-f5f8-466e-aff9-25556b57fe6d </tt> </td>
<td> Estimote </td>
</tr>
</tbody>
</table>
<p> The above highlights that although all iBeacons must, by definition, transmit Apple's company code (<tt>0x004c</tt>), they are not necessarily Apple devices! In general: </p>
<blockquote> it is wise to <i>not</i> assume that a device advertising a specific company code is necessarily a product of that company. </blockquote>
<h3> Local Name </h3>
<p> A Local Name is an <b>ASCII string</b>. The Local Name is often human-readable (ex: "Charge HR") as the formats described above afford more efficient encoding of machine-readable identifiers. The length of this name is limited by the capacity of the BLE payload. </p>
<p> </p>
<div class="well">
<h2> Additional resources and tools </h2>
<p> </p>
<ul class="media-list">
<li class="media">
<div class="media-left">
<img class="media-object" src="diy/best-practices-ble-identifiers/images/icon.png">
</div>
<div class="media-body">
<h4 class="media-heading">
<a href="diy/best-practices-ble-identifiers/"
target="_blank">
Best practices for BLE identifiers
</a>
</h4>
<p> Assignment of Bluetooth Low Energy identifiers for interoperability and interpretability </p>
</div>
</li>
<li class="media">
<div class="media-left">
<img class="media-object" src="/interoperable-identifier/images/icon.png">
</div>
<div class="media-body">
<h4 class="media-heading">
<a href="interoperable-identifier/" target="_blank">
The InteroperaBLE Identifier
</a>
</h4>
<p> An open specification by reelyActive to maximise the interoperability of radio-identifiers across protocols, platforms and operating systems. </p>
</div>
</li>
<li class="media">
<div class="media-left">
<img class="media-object" src="diy/common/images/icon.png">
</div>
<div class="media-body">
<h4 class="media-heading">
<a href="/" target="_blank">
reelyActive Developers
</a>
</h4>
<p> Browse all developer documentation and tutorials. </p>
</div>
</li>
</ul>
<p> For an exhaustive machine-readable list of common BLE UUIDs see <a href="https://github.com/reelyactive/sniffypedia/blob/master/index.js" target="_blank">Sniffypedia's index.js</a> </p>
</div>
<hr>
<h2> What's next? </h2>
<p> Explore Sniffypedia, check out advlib, or return to the diyActive home page. </p>
<p class="text-center">
<a class="btn btn-default" href="https://sniffypedia.org"
role="button"> Sniffypedia </a>
<a class="btn btn-default" href="https://github.com/reelyactive/advlib#advlib"
role="button"> advlib </a>
<a class="btn btn-success" href="/"
role="button"> Return to diyActive </a>
</p>
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