Abstract. This paper reports the first use of ID Modulation to embed a bitstream representing sensor information in a standards-compliant Radio Frequency Identification (RFID) channel. Like other forms of information hiding, ID Modulation embeds a new, lower bit-rate channel in a pre-existing host channel, without requiring any changes to the protocols defining the host channel. Like most other forms of information hiding, the embedded data is represented as correlations introduced into the host channel data stream. Most previous applications of information hiding have emphasized either secrecy (as in steganography) or robustness to removal (as in watermarking). The benefit of information hiding that is most important for the application reported here is backward compatibility with pre-existing standards and hardware. It has allowed us to build a new communication layer (for transmitting sensor data) on top of current RFID infrastructure.