data center aisle with a RAIN RFID reader powering a battery‑free UHF sensor tag

“Battery‑free” doesn’t mean “no energy.” It means sensors harvest energy on demand (often from sub‑1 GHz RF) and buffer it (e.g., in capacitors/supercapacitors) to take a measurement and backscatter the data. That subtle difference is what makes deployments practical, compliant, and maintenance‑free.