We propose a new biometric based on the human body's response to an electric square pulse signal, called pulse-response. We explore how this biometric can be used to enhance security in the context of two example applications: (1) an additional authentication mechanism in PIN entry systems, and (2) a means of continuous authentication on a secure terminal. The pulse-response biometric is effective because each human body exhibits a unique response to a signal pulse applied at the palm of one hand, and measured at the palm of the other. Using a prototype setup, we show that users can be correctly identified, with high probability, in a matter of seconds. This identification mechanism integrates well with other established methods and offers a reliable additional layer of security, either on a continuous basis or at login time. We build a proof-of-concept prototype and perform experiments to assess the feasibility of pulse-response as a practical biometric. The results are very encouraging, achieving accuracies of 100% over a static data set, and 88% over a data set with samples taken over several weeks.