Despite decades of research on battery-free systems, their adoption in everyday electronics remains limited. Interactive Internet of Things devices such as wearables, personal trackers, and health monitors are increasingly widespread, yet almost all depend on batteries that are environmentally harmful, slow to charge, and have limited lifespans. Existing battery-free devices have seen use only in niche applications with minimal user interaction, primarily due to slow energy harvesting, frequent power interruptions, and restricted sensing capabilities under tight energy constraints. To address these limitations, we present Cheetah, a battery-free architecture that charges rapidly and reliably from ubiquitous wireless chargers, reduces power consumption, and enhances usability. We implement and evaluate Cheetah architecture as a smartwatch and a wearable patch, capable of operating for a full day after only six seconds of charging. Our results demonstrate that battery-free design can move beyond niche deployments to become a practical and sustainable alternative for mainstream interactive electronics. ... Read more

Continuous monitoring of vital signs has become increasingly important for digital healthcare and enhancing self-awareness. Wearable devices like smartwatches, earbuds, and rings are gaining widespread acceptance for health monitoring. However, two significant challenges remain: (i) the limited battery life of these devices makes them unsustainable for long-term use, and (ii) many older adults, who would benefit most from health monitoring, often face barriers due to limited digital literacy. To address these issues, we introduce BioPulse---a perpetual, patch form-factor device designed for continuous monitoring. BioPulse estimates key parameters for cardiac health such as heart rate, heart rate variability, and blood pressure. By utilising a sparse sampling algorithm alongside NFC-based energy transfer and communication, the system operates without a battery, achieving a 57.9% reduction in power consumption. The system demonstrates a mean absolute error of 5.6 mmHg for systolic blood pressure (SBP) and 4.5 mmHg for diastolic blood pressure (DBP) compared to the ground truth device. This combination ensures a more sustainable and accessible solution for vital signs monitoring. ... Read more

Continuous vital sign monitoring is essential for digital healthcare and self-awareness but is hindered by the limited battery life of wearable devices and barriers faced by older adults with low digital literacy. BioPulse, a battery-free patch device, addresses challenges in vital sign monitoring by using sparse sampling and NFC energy transfer to track heart rate, HRV, and blood pressure. ... Read more