The Codatex RFID Sensor works with 125 kHz transponders and can read five-byte transponder numbers into the NXT Intelligent Brick. The RFID Sensor has three different reading modes: single read, continuous read, and stop. The maximum reading distance depends on the transponder size; for example, the keyfob will read up to a maximum distance of 30 mm. One RFID Sensor, five keyfob transponders, five clear disc transponders, and two card transponders are included in this set. Requires NXT firmware 1.05 or later. For more information about the RFID Sensor, programming examples, and to download the programming block, visit www.LEGOeducation.us/codatex.