This paper presents a novel and straightforward architecture for a batteryless sensor tag. The tag consists solely of a 25x25 mm2 spiral antenna used for both wireless power transfer and back telemetry (at 13.56 MHz), along with capacitors, diodes, a transistor, and a transducer element. Due to its operation at high frequency (HF), the proposed system can be used in applications where the surroundings exhibit significant absorption hindering the use of UHF tags. The proposed proof-of-concept prototype employs a thermistor as the transducer element, enabling temperature sensing in a range of −5 to 45 degrees Celsius, achieving reading distances of up to 60 cm.