This paper presents the architecture and design trade-off of a compact, programmable, battery-less UHF-RFID sensor tag for environmental monitoring. The node is based on a single UHF monopole matched to a dual-path rectifier for both energy harvesting purposes and wake-up radio capabilities. The based-band circuit includes a power management unit (PMU) to supply the microcontroller unit which is in charge of implementing the EPC Gen 2 Class 1 standard protocol fully working with European ETSI compliant readers. The prototype was built with off-the-shelf components in a 95x31 mm 2 PCB with low losses Rogers 4350B substrate. The proposed circuit can wake-up starting from a fully discharged state and operate at distances up to 9.70 m from a 2W ERP source in the UHF 865-868 MHz frequency band, with a power sensitivity of -16 dBm, while performing temperature sensing and radio-frequency communication. If an on-board battery is added, the batteryassisted solution is able to work as far as 15 m from the interrogator reaching the highest sensitivity of -17.8 dBm while the energy harvesting circuits replenishing the battery.