PicoTag: Enabling Generalized and Robust RF-Insensitive Sensing on COTS RFID Tags

RFID offers a promising foundation for sensing due to its low cost, battery-free operation, and wide commercial deployment. However, sensing RF-insensitive parameters typically requires specialized circuits or hardware modifications to RFID tags, limiting scalability and practical adoption. In this paper, we present PicoTag, a novel design paradigm that seamlessly transforms commodity RFID tags into versatile sensing nodes capable of detecting RF-insensitive environmental parameters. Implemented as a low-cost, low-power add-on patch, PicoTag leverages electromagnetic coupling effects to operate alongside unmodified RFID tags. Specifically, we design a new framework capable of integrating impedance-sensitive media from prior work, thereby enabling generalized sensing. For robust parameter reading, we further introduce a passive reference-signal generation circuit that enables calibration, compensating for link coefficients and hardware variations. Importantly, PicoTag is fully compatible with COTS RFID communication protocols and introduces no interference to existing RFID systems. We develop a complete hardware prototype of PicoTag and evaluate its performance across a range of sensing tasks and deployment scenarios. The results show that the power consumption of PicoTag is 15µW, achieving an average temperature sensing error of just 0.9°C while maintaining consistent performance across different tags, deployment environments, and distances. The hardware schematics can be found at: https://doi.org/10.5281/zenodo.18085137.