A method for facilitating biometric security in a transponder-reader transaction system is provided. The method includes determining if a transaction violates an established rule, such as a preset spending limit. The method also includes notifying a user to proffer a biometric sample in order to verify the identity of said user, and detecting a proffered biometric at a sensor to obtain a proffered biometric sample. The method additionally comprises verifying the proffered biometric sample and authorizing a transaction to continue upon verification of the proffered biometric sample.