IMSI Catcher (Stingray)

An IMSI catcher — commercially known by the brand name Stingray — is a portable device that broadcasts a signal mimicking a legitimate mobile base station. Because phones are designed to connect to the strongest available signal, they attach to the IMSI catcher and transmit the unique identifier (IMSI) stored on the SIM card. The operator can then track the phone's location, intercept unencrypted calls and SMS messages, and in some configurations block or downgrade service to force the phone onto 2G where encryption is weaker.

IMSI catchers are used by law enforcement with varying legal oversight, but identical or equivalent technology is also used by criminal actors, state-level intelligence services, and corporate espionage operatives. For ordinary consumers, the risk is most acute in high-value targets: executives, journalists, activists, and individuals carrying financial credentials or sensitive communications.

Protection involves using apps with end-to-end encryption for calls and messages (which IMSI catchers cannot decrypt), being alert to unusual battery drain or loss of service, and using devices that support detection tools. Switching to a 5G-only plan reduces vulnerability because 5G has stronger base-station authentication that mitigates some IMSI-catcher techniques.