Janus: Efficient and Accurate Dual-radio Social Contact Detection

Determining when two individuals are within close distance is key to contain a pandemic, e.g., to alert individuals in real-time and trace their social contacts. Common approaches rely on either Bluetooth Low Energy (BLE) or ultra-wideband (UWB) radios, that nonetheless strike opposite tradeoffs for energy efficiency vs. accuracy of distance estimates. Janus reconciles these dimensions with a dual-radio protocol enabling efficient and accurate social contact detection. Measurements show that Janus achieves weeks to months of autonomous operation, depending on the configuration. Several large-scale campaigns in real-world contexts confirm its reliability and practical usefulness in enabling insightful analysis of contact data.