A frequency-encoded smart contact lens (SCL) is introduced for in situ eye tracking and wireless human-machine interaction (HMI). The SCL, which is chip-free, battery-free, and biocompatible, uses a frequency encoding strategy and advanced spherical conformal preparation technique to detect eye movement and closure. It features high angular accuracy of less than 0.5°, which is even less than the central fovea's vision range. The SCL supports multiple HMI applications, including eye-drawing, the Gluttonous Snake game, web interaction, pan-tilt-zoom camera control, and robot vehicle control. Comprehensive biocompatibility tests show low cytotoxicity and low eye irritation, making the SCL suitable for long-term wear. The SCL is designed to be imperceptible and lightweight, enabling seamless integration with wearable devices. The system uses a portable sweeping-frequency reader to collect signals from four RF tags with different working frequencies, enabling precise tracking of eye movements and closure. The SCL has been tested in vivo on rabbits, demonstrating its ability to control a robot vehicle wirelessly and showing no significant corneal irritation. The SCL's high accuracy, robustness, and biocompatibility make it a promising tool for advancing eye tracking technology and HMI applications. The study highlights the potential of the SCL for various applications, including medical diagnosis, cognitive science research, and consumer experience research. The SCL's design and performance suggest that it could revolutionize the way humans interact with machines through eye tracking.A frequency-encoded smart contact lens (SCL) is introduced for in situ eye tracking and wireless human-machine interaction (HMI). The SCL, which is chip-free, battery-free, and biocompatible, uses a frequency encoding strategy and advanced spherical conformal preparation technique to detect eye movement and closure. It features high angular accuracy of less than 0.5°, which is even less than the central fovea's vision range. The SCL supports multiple HMI applications, including eye-drawing, the Gluttonous Snake game, web interaction, pan-tilt-zoom camera control, and robot vehicle control. Comprehensive biocompatibility tests show low cytotoxicity and low eye irritation, making the SCL suitable for long-term wear. The SCL is designed to be imperceptible and lightweight, enabling seamless integration with wearable devices. The system uses a portable sweeping-frequency reader to collect signals from four RF tags with different working frequencies, enabling precise tracking of eye movements and closure. The SCL has been tested in vivo on rabbits, demonstrating its ability to control a robot vehicle wirelessly and showing no significant corneal irritation. The SCL's high accuracy, robustness, and biocompatibility make it a promising tool for advancing eye tracking technology and HMI applications. The study highlights the potential of the SCL for various applications, including medical diagnosis, cognitive science research, and consumer experience research. The SCL's design and performance suggest that it could revolutionize the way humans interact with machines through eye tracking.