Personal RFID tags store valuable information private to their users that can easily be subject to eavesdropping, unauthorized reading, owner tracking, and cloning. RFID tags are also susceptible to relay attacks and likely to get lost and stolen. In this paper, we introduce the problem of user authentication to RFID tags. This allows users to control when and where their RFID tags can be accessed. We present a novel approach for user authentication to multiple RFID tags called “Vibrate-to-Unlock” (VtU). This technique uses a mobile phone as an authentication token, forming an unidirectional tactile communication channel between users and their RFID tags. Authenticating to an RFID tag involves touching a vibrating phone to the tag or an object carrying the tag, such as a wallet. We discuss the design and implementation of this new method on Intel's WISP tags. We also report on a preliminary usability evaluation of our VtU prototype.