Radio-Frequency Identification (RFID) systems are becoming increasingly used within smart environments. In this paper, we propose BitID, a passive Ultra-High Frequency (UHF) RFID based sensing technique that can easily be made using off-the-shelf tags. BitID can be added to everyday objects to enable sensing and control capabilities. With a simple shorting mechanism, BitID is able to differentiate between two states of the object to which it is attached (for example, whether a door is open or closed). We explain the working principle of BitID, and demonstrate how to build and apply it to target objects. We also show that by using a three layered system architecture, BitID can be used for various applications, including event detection, energy monitoring, fitness tracking, human behavior tracking and control.