It's because they use the devices for eavesdropping. If they want to use data they collected from eavesdropping in court, then they need a warrant.
For example, if they're spying on a drug dealer, they can determine the right time to pull them over for a traffic violation and also catch them in the act of transporting drugs. If law enforcement doesn't submit evidence obtained from spying, it looks like whoever pulled them over was just in the right place at the right time[1].
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It's because they use the devices for eavesdropping. If they want to use data they collected from eavesdropping in court, then they need a warrant.
For example, if they're spying on a drug dealer, they can determine the right time to pull them over for a traffic violation and also catch them in the act of transporting drugs. If law enforcement doesn't submit evidence obtained from spying, it looks like whoever pulled them over was just in the right place at the right time[1].
[1] https://en.wikipedia.org/wiki/Parallel_construction
I see. Do newer 3gpp/ETSI standards take this kind of surveillance into account? Surely this must not work for intercepting VoLTE or 5g voice calls?