As smartphone users have become more aware that fake cell phone towers, known as IMSI catchers or stingrays, can spy on them, developers have rushed to offer apps that detect when your phone connects to one. Unfortunately, it seems, those tools aren't as effective as they claim. Watching the watchers turns out to be a complicated business. Researchers from Oxford University and the Technical University of Berlin today plan to present the results of a study of five stingray-detection apps.

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