If you’re traveling abroad on business, there’s a good chance you’ll need to bring along a smartphone to get around, meet up with associates or learn about the idiosyncrasies of local culture. But even if you’re security-savvy and never let your device out of sight or engage in risky activities like connecting to WiFi, local intelligence services can monitor you through your cellular connection alone. Knowing how this happens will help you mount an effective counter-defense the next time you land on foreign soil.