Traditional testing of IoT device software can leave subtle bugs undetected, leading to vulnerabilities. Today's formal methods mathematically guarantee code security and quality, and the absence of bugs. Over the last decade, mathematical methods have been democratized to go beyond formal verification of mission-critical software applications in industries like aeronautics. This NIST-recognized technology is now mass-market. It is increasing the security and code quality of devices like smartphones, game consoles, and smart meters. This presentation will introduce how formal methods differ from traditional testing and the benefits they bring in practical applications for connected devices.