Many options exist for prototyping software-based human-computer interfaces, but there are few comparable technologies that allows application developers to create ad-hoc hardware interfaces with corresponding ease and flexibility. In this paper, we present a system for rapidly constructing low cost prototypes of mobile input devices by leveraging wireless sensor nodes. We demonstrate two proof-of-concept applications -a conductor's baton and a scene navigation controller-that are prototyped using wireless sensor networks. These applications illustrate that wireless sensor technology can be used to quickly and inexpensively prototype diverse physical user interfaces. We believe that this technology will be of value in many areas, including the study of ergonomics, haptic interfaces, collaborative design, low-cost VR systems, and usability research.