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Ask Slashdot: How To Stay Ahead of Phone Tracking ?

Posted by samzenpus on from the watching-the-watchers dept.

An anonymous reader writes "In the last few years there has been a significant upsurge in subverting the cellular network for law enforcement purposes. Besides old school tapping, phones are have become the ideal informant: they can report a fairly accurate location and can be remotely turned into covert listening devices. This is often done without a warrant. How can I default the RF transmitter to off, be notified when the network is paging my IMSI and manually re-enable it (or not) if I opt to acknowledge the incoming call or SMS? How do I prevent GPS data from ever being gathered or sent ?"

6 of 259 comments (clear)

  1. Don't carry one by siddesu · · Score: 5, Informative

    As you know, they can track you even when the device is off, unless you've taken the battery out.

    1. Re:Don't carry one by Electricity+Likes+Me · · Score: 4, Informative

      If you really want to track someone, it's usually way easier to steal and modify their phone, or modify a replica phone and download their phone to that one.

      There are a lot of high-tech surveillance techniques, but they're just really kind of hard to do compared to the simple stuff.

  2. Transmitter off won't work. by rew · · Score: 5, Informative

    If you want to receive calls or SMSes, you need to leave the phone on and transmitting:

    When a call for your number comes in, the incoming call is NOT transmitted nationally. Only in the GSM-cell that you are actually in is the signal transmitted. So, the system has to know in which cell you are to be able to "call" your phone. If you properly turn it off, the phone will tell the GSM network it is going off. So when a call comes in, it will go to voicemail immediately. If you yank the battery, the system will assume you are still in that cell where you last had the phone on, but it will probably time you out if it doesn't hear from your phone for a while. (which happens naturally if for example you drive out of range).

    1. Re:Transmitter off won't work. by KiwiSurfer · · Score: 5, Informative

      When a call for your number comes in, the incoming call is NOT transmitted nationally. Only in the GSM-cell that you are actually in is the signal transmitted. So, the system has to know in which cell you are to be able to "call" your phone.

      Not quite, a GSM switch will keep track of which Location Area (LA) a mobile device is in. A LA can contain a few or upwards to several hundred cells. Using Vodafone's GSM network in New Zealand as a point of reference, their largest LA covers all of Auckland's (our biggest city with 1.5m population) CBD with around 150-200 sites while in rural areas a LA generally only has around 50 sites.

      When a phone is being called, all the cells in the LA will send out a broadcast request to all mobile devices in the LA and the mobile device will respond by contacting the nearest cell. This is quite useful as it reduces the need for the mobile device to check in frequently — the mobile device only needs to check in with the network when it moves into a new LA.

      I'm not too familiar with how UMTS or LTE works but I presume the same principles applies but I may stand corrected.

  3. Airplane mode and OsmocomBB by asnelt · · Score: 5, Informative

    I would say a good start is to just use the airplane mode of your phone. That should disable your RF transmitter. But of course you wont be notified when the network is paging your IMSI. The save option is to use a phone with OsmocomBB, a free software implementation of the GSM stack: http://bb.osmocom.org/trac/ It has limited functionality (no GPRS working at the moment) but at least you know exactly would your phone is doing. With that, you can even run CatcherCatcher, which is able to detect IMSI catchers: http://opensource.srlabs.de/projects/catcher The supported phones are a bit outdated, mostly old Motorola phones. But there is one supported smartphone: the Openmoko Freerunner. It is pretty usable these days and is fully supported by Debian. I love it, but you will need to tinker - a lot.

    1. Re:Airplane mode and OsmocomBB by asnelt · · Score: 5, Informative

      What I forgot to mention: using OsmocomBB it should even be possible to fake your location. It is explained in this presentation at 05:20: http://www.youtube.com/watch?v=M0NjS6aUXYw