In this work, we describe a low-power transponder based on a Texas Instruments MSP430 microcontroller which interfaces both with sensors and with a passive, 13.56 MHz RFID front-end. This prototype features commercial RH, temperature light sensors. We tested the correct operation of the transponder using a commercial reader compliant to the ISO-15693 directives. The implemented commands are correctly managed using a pulse position coding 1 out of 4, a 100% ASK modulation from reader to transponder and a high data rate from transponder to reader.