How it works

Android Emergency Location Service (ELS) is a supplemental service that sends enhanced location directly from Android handsets to emergency services when an emergency call is placed.

Today, ELS works on over 99% of active Android devices (running Android OS version 4.0 /Ice Cream Sandwich and above). It is not a mobile application that the user has to download and install, but is instead built into Google Play Services as part of the Android operating system.

Benefits of ELS

  • ELS doesn't require any special hardware, downloads or updates.
  • ELS is activated only when the user contacts Emergency Services.
  • Location is computed on the handset and sent to Emergency Services.
  • Location data is sent via Data SMS (per AML specifications) or HTTPS, which are both open, OS-agnostic protocols.
  • ELS location is often more accurate and reliable than cell tower IDs.

Google will activate ELS once a mobile network operator or emergency infrastructure provider has built the necessary endpoint to receive emergency location.

Google does not charge for ELS, nor do we store any ELS location data. Our goal is make it easier for first responders locate Android users in an emergency, and improve the state of emergency services around the world.

How ELS computes location:
Data flow and quality

Computing location

The user’s location is computed locally and sent directly from the handset to an endpoint maintained by the mobile network operator/PSAP (Public Safety Answering Point or emergency call center), never through Google servers.

Location information is sent only when the user dials emergency services (many countries already mandate that location be sent during an emergency call; ELS provides a more accurate location estimate during these emergency situations).

Location quality

In many countries today, emergency call centers only receive cell-based location, with a location radius on the order of kilometers. In other countries, location during emergency calls is estimated using GPS, falling back to cell -- but GPS only works well in good satellite line-of-sight conditions (i.e., outdoors) but not so well indoors, underground or in urban canyons (city centers with tall buildings).

With ELS, when a user contacts a configured emergency number from a handset, the device automatically activates ELS to send location information. This happens via a high accuracy location request that is registered with the Android Fused Location Provider. FLP allows us to derive a more accurate indoor or outdoor location as quickly as possible using a variety of sensors.

While no one can guarantee completely accurate location data, we are always working to improve the quality of our location services. The location provided by ELS is the same location seen on Android devices every day, through Google Maps and other location based apps and services. In many cases, ELS can be significantly faster and more accurate than location obtained through cell towers and GPS alone. For example, British Telecom in the UK has reported a radius of 50 meters or less for most ELS calls (about 85% of locations), and in some situations has reported receiving location information before the call is even connected!

2016 UK Live Test Results

Endpoints: How ELS reports location

In order to work, ELS requires at least one "endpoint" to receive location information, currently either a SMSC or HTTPS server.

The endpoint(s) receives messages with ELS location data from an Android handset calling an emergency number, and relays the information to emergency call takers in a PSAP (Public Safety Answering Point, i.e., call and dispatch control for emergency services). It is the partner's responsibility to create and maintain the endpoint.

ELS currently supports two reporting methods to the endpoint: Data SMS and HTTPS Post. It’s important to understand the difference between the two options, as there are tradeoffs involved.

Note

Data SMS is a subset of the SMS protocol which allows for binary data to be sent to specific ports at endpoints (it has nothing to do with a cellular 'data' connection). ELS transmits over Data SMS in the AML format while HTTPS transmits location information as an HTTPS POST request, using Google's format.

The table below outlines advantages and disadvantages for each, although most partners have found Data SMS to be more reliable (failure rates are approx ⅓ lower than HTTPS).

Data SMS HTTPS
Description Subset of the SMS standard for binary data that is addressed to a specific port on a device. Data SMS contains arbitrary binary information rather than formatted text. HTTPS server that can handle POST requests. Emergency location is transmitted as a POST request with information in key/value pairs.
Advantages
  • Doesn’t require a data connection
  • More reliable, lower failure rate (may vary by country)
  • Message won’t show up in user’s SMS outbox
  • More secure
  • Unlimited size (can transmit more information than Data SMS, e.g. altitude, device model, etc)
  • Easy to set up
Disadvantages
  • May be more difficult to set up SMSC to correctly handle data SMS
  • Not visible to other apps but still unencrypted over the network
  • Requires a data plan
  • Less reliable (varies by country)—unreliable on bad connection, higher failure %, unable to retrieve MSISDN if not stored on SIM card
  • Doesn’t work on CDMA network

How to Become an ELS Partner

We partner with government, mobile network operators, PSAPs/emergency services, or other entities already responsible for handling emergency call connections in order to deploy ELS in a given country or region. In most countries, existing emergency center infrastructure can be utilized, and in many cases, one endpoint is sufficient to utilize ELS in an entire country.