Locating and Tracking Mobile Phones

There is a lot of misinformation around about tracking mobile phones, what is possible and what is practical. I wrote this post in answer to a number of questions and discussions on the Bristol LUG mailing list, and I think it could do with a wider audience.

Lets look firstly at locating a 2G mobile that is not in a call. In this case the network will know that last area code (LAC) for the mobile, when the mobile moves out of that LAC, then it performs a location update to update the information in the VLR as to which LAC it is now in.

A location update can also be triggered by the network, network sends a page to the control channel of all the sites in the LAC, and it can also be triggered by the mobile on a number of parameters.

The location of the mobile is measured in the phone in relation to the cell tower, all 2G phones need to measure their distance from the serving site in order to ensure that when they transmit in their allocated slot the propagation delay to the site is taken account. Phones can also measure their distance from several sites to then triangulate their position more accurately. This is an optional feature and requires the installation of a location server in the network to make it work. Not aware of any UK networks who have installed this service.

When a connection is established, be it call, text or data, the creation of a Call Detail Record (CDR) is started, this will contain the cell ID of the serving site for the call initiation, and this record is then “cut” completed by some subsequent events such as ending the call, or some handover events etc. So the location of the cell that the call started in is recorded and can be examined.

The phone itself and hence software on the phone will always be able to see the list of neighboring cells and their signal strength, and if in a call the measured distance to the serving cell from the delay measurement. So Google maps is able to say where you are to the accuracy of the serving cell and distance.

When calls are made to emergency services in the UK the location is reported to the accuracy of a list of regions, these approximately relate to groups of LAC areas. Certainly not more accurately than that.

When a interception warrant is made on a subscriber the network monitoring tools can be used to monitor events relating to the phone, so any location update messages received would include the cell id even though this is not recorded in the VLR, just the LAC. and silent ping messages can be sent to the phone to get it to send a location update at any time.


5 Responses to Locating and Tracking Mobile Phones

  1. Roger Shepherd says:

    Very interesting description of the capabilities of location using 2G technology. In a phone with wifi there are other capabilities based on using the MAC of an access point to determine location via a geolocated database. This seems to work quite well.

    • Stuart says:

      Yes but this is still under the control of the mobile, the MAC address needs to be collated with an actual physical location, but given several MAC addresses this can be done with a degree of certainty, especially where phones that have GPS also report their GPS location and the MAC addresses so that the databases can be updated.

      But unless there is software on the phone reporting this the location of the phone cant be tracked from WiFi MAC addresses.

  2. Stuart says:

    This is a different aspect of location information. I was talking about what is available in the network without your knowledge and consent. This advise is clearly useful in protecting the location information that you voluntarily release, and what can happen to this.

  3. Britney says:

    Yesterday, while I was at work, my cousin stole my iPad and tested to see if it can survive a 30
    foot drop, just so she can be a youtube sensation.
    My apple ipad is now destroyed and she has 83 views.
    I know this is completely off topic but I had to share it with someone!
    Many thanks, to you!

  4. Greetings! Very helpful advice in this particular article!

    It’s the little changes that produce the most significant changes.
    Many thanks for sharing!

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