We are rapidly moving toward a pervasively-sensed wireless world where most of our interactions with machines will be accomplished via gestures, and machines will be able to recognize human activities and pinpoint human/object locations. Wireless sensing, tracking, and drawing technologies are among the key enabling factors in this pervasively-sensed world. In this talk, I will present my recent works on RFID based sensing systems. The first work is our tag order tracking systems - STPP, which leverages the spatial-temporal phase correlation to determine the tag order in 2D space without locating each tag a prior. The second work, MobiTagbot, improves the tag ordering accuracy to a great extent by minimizing the impact of multi-path effect indoors. The third work, PolarDraw, is a RFID tracking system that enables in-air writing with only two antennas. As an extension, I will also talk about our single antenna based human-object interaction system.