[ Previous Tech&Sec articles can be found on our website: https://unoffensiveanimal.is/category/technology-security-101/ ]
In the last episode we talked about burner phones and that you should not turn them on next to your personal phone. Today, we are going to discuss IMEI and IMSI, which should explain not only WHY you shouldn’t do that, but also why you should consider what other devices are around yours when you have your phone on!
IMEI and IMSI are both ID numbers. Whilst there are ways of spoofing them (making them different), they are not common for everyday activists, and for all purposes in this article we will understand IMEI and IMSI as unchangeable IDs, like human fingerprints! IMEI is the fingerprint ID of your device (a phone, a wifi camera, a tracker), whilst IMSI is the fingerprint ID of the SIM card installed in that device. If you have a phone and change the SIM card, your IMEI number will stay the same. If you buy a new phone but still use the same SIM card as before, you are transferring the IMSI number to a different device.
Both numbers are used by cell companies to identify who is requesting a call or a text or the use of data. They also have another use which is a lot more concerning for our privacy and security. Using those IDs, cell companies can triangulate the location of your device, even if the location is turned off in your smartphone! The accuracy of the triangulation will depend on how many towers your device is able to connect to, which makes things somewhat easier in more built up areas where there are more towers and a little more difficult in the countryside, where the triangulation MIGHT give a much more general location.
This location triangulation is used by the police regularly in order to establish if YOU were at a specific location or not, or, in case of less common locations, they are able to check what devices where in the area at a specific time to narrow down the investigation to a few people.
If you pay for your phone with anything other than cash, the IMEI and IMSI of your devices is connected to your bank account, which means it is connected to your name and potentially your address. This is why we always recommend to NEVER pay for phone credit (or any other cell service) with anything but cash.
It is also worth noting that the IMEI and IMSI numbers can be used to create association of devices. Let’s say you want to meet with a friend, and you both take the phone with you, but leave it in your respective cars before going for a walk and a chat. If the cars are parked near each other, the filth is now able to deduce you two met. Equally, if someone is doing an investigation and uses a tracker, the tracker too has IMEI and IMSI IDs, so if they travel with their phone and the tracker on, those two devices are being registered by the cell towers as “together”.
Here are a few bits of advice:
- If you must take your phone with you but you do not want the cell towers to triangulate your location, consider turning it off AND putting it inside of a faraday bag well away from your meeting point. This should stop all connectivity, thus stopping the tracking of the IMEI/IMSI.
- Both SIMs and devices should be recycled regularly. Your IMEI creates a map of your locations and a map of your relationships, so sell your phone every six months and get a different one. If you’re buying used, you should manage to buy/sell with little loss or maybe a little profit! You should do the same with your SIM card and never transfer your actual telephone number. They should be refreshed at the same time.
- Don’t carry trackers or wifi cameras or other SIM devices alongside your phone unless you are isolating them separately with faraday bags.
Stay safe, and stay dangerous!
Your local anarchist cyber-counsellor.