This is a description taken from LEGO.com. Do not modify it.
Add even more functionality to your MINDSTORMS NXT RF ID Sensor (sold separately) with 10 additional keyfob transponders! Requires MS1048 RF ID Sensor, sold separately. This is the individual component, and does not include the NXT Intelligent Brick, software or any accessories. It requires the complete LEGO MINDSTORMS NXT set (#8527) for use.