Matt Blaze over at Exhaustive Search has an interesting post on how law enforcement agencies track phone calls. Blaze is discussing law enforcement targeting individuals in support of criminal investigations not the wholesale dragnet surveillance of the type that the NSA specializes in.
If you’re the type that likes cop shows you’re already familiar with some of these techniques. There’s what Blaze calls the retrospective methods that subpoena call detail records from the phone company. There’s also real time methods where the authorities capture call information as the calls happen. Again, many of these—such as pen registers—are part of popular culture and well known to devotees of police procedurals.
What’s more interesting are the lessor know methods such as tower dumps, 911 pings, and IMSI catchers. Blaze explains what these are and how they work.
While there is some controversy over a couple of these methods—especially the IMSI catchers—most people see these techniques as legitimate investigative tools unlike the highly controversial wholesale surveillance used by the NSA. Still, if you’re concerned about privacy and how the government might, legitimately or illegitimately, track your communications, you will find this post helpful.