We present an ISO18000-6C (EPC Generation 2) compatible battery-free RFID tag designed for a hazardous material monitoring application. This tag is a wirelessly powered sensor device that incorporates a general purpose microprocessor to enable the development of specialized sensor applications. It is housed in a ruggedized enclosure that incorporates a dual-polarized 6 dBi antenna for the 902-928 MHz UHF RFID band. It integrates two custom UHF RFID analog front end ASICs with a general purpose TI MSP430 microcontroller and a fiberoptic tamper detection loop. The tag has a power-up threshold of +3 dBm due to the power requirements of the fiber-optic tamper detection loop. It has a measured operating range of over 5.5 m with a +36 dBm EIRP EPC Generation 2 reader.