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On a recent television show, on ID Discovery, 'The Case that Haunts Me' (season 3 epi 4 'Cruel and Unusual') the lead detective finds out that the prime suspect has taken the SIM card out of his phone and put it in his murdered wife's phone...

I thought only the SIM card could be traced/tracked...

How could someone tell, without ever having seen (or seized) the phone(s), if SIM cards have been switched?

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  • \$\begingroup\$ Your question is valid. But TV depiction of technology is usually pretty shitty. If you want to have a fun time, ask a person who had a basic signal processing course about how CSI does their "enhance that license plate" technology... \$\endgroup\$ Jun 26, 2020 at 8:50
  • \$\begingroup\$ Yeah, TV gets it wrong so often. I love it when they show "IP addresses" like "456.976.278.23". I mean, they could use the "192.0.2.0–192.0.2.255" range. People who know something about IP would understand and most viewers wouldn't care. Kind of like the "555-" telephone number used in American movies and TV shows. \$\endgroup\$
    – JRE
    Jun 26, 2020 at 9:17
  • \$\begingroup\$ @JRE As I understand it, the use of invalid numbers like this is intentional. It is done to prevent innocent people from being overwhelmed by idiots trying to call the number they see on TV. This happened, for example, after Tommy Tutone released the hit song "867-5309/Jenny". \$\endgroup\$ Jun 26, 2020 at 13:26
  • \$\begingroup\$ @ElliotAlderson: Exactly. The phone company explicitly never issues 555- numbers so that they can be used that way. In the same way, the IETF reserved the range 192.0.2.0–192.0.2.255 for documentation only. You use them as examples when writing the documentation, and since they will never be assigned you cannot contact them and will cause no conflicts if some lunkhead accidentally copies one from the docs to the real system. Since they'll never be used IRL, they are perfect for fiction - but still look real. \$\endgroup\$
    – JRE
    Jun 26, 2020 at 13:35

3 Answers 3

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The SIM card has an international mobile subscriber identity (IMSI) that is used to tell who is calling. SIM cards identify the owner.

The phone has an international mobile equipment identity(IMEI) that is used to identify the phone.

Both are used at various times when a phone is connected to a network. That information will be stored for some length of time for billing and other purposes.

If you have the authority (court order and such) then the network operators can tell you which IMSI was used with which IMEI, and when (provided they still have the records.)

You could then match the IMEIs of the two people to the IMSI of the one person and see when each combination was used.

If all you have is the IMSI, then you can still get the records. If the SIM is used for a long time with one particular IMEI, then changes to a different IMEI at about the time the murder (or whatever) occurred, then you have a hint that the killer may have swapped the SIM.

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The SIM contains the IMSI and the phone contains IMEI, if the phone registered to a network, this combination is logged.

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Law enforcement can get access to the mobile network operator's infrastructure. (laws governing how that's regulated differ wildly.)

Without that access, none can be done remotely.

With that access, you get access to everything the cellular network. That of course includes the subscriber data (IMSI) as well as phone data (IMEI etc).

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