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A new approach to ubiquitous sensing for indoor applications is presented, using low-cost indoor perovskite photovoltaic cells as external power sources for backscatter sensors. Wide-bandgap perovskite photovoltaic cells for indoor light energy harvesting are presented with the 1.63 and 1.84 eV devices that demonstrate efficiencies of 21% and 18.5%, respectively, under indoor compact fluorescent lighting, with a champion open-circuit voltage of 0.95 V in a 1.84 eV cell under a light intensity of 0.16 mW cm −2 . Subsequently, a wireless temperature sensor self-powered by a perovskite indoor lightharvesting module is demonstrated. Three perovskite photovoltaic cells are connected in series to create a module that produces 14.5 µW output power under 0.16 mW cm −2 of compact fluorescent illumination with an efficiency of 13.2%. This module is used as an external power source for a battery-assisted radio-frequency identification temperature sensor and demonstrates a read range by of 5.1 m while maintaining very high frequency measurements every 1.24 s. The combined indoor perovskite photovoltaic modules and backscatter radio-frequency sensors are further discussed as a route to ubiquitous sensing in buildings given their potential to be manufactured in an integrated manner at very low cost, their lack of a need for battery replacement, and the high frequency data collection possible.