This paper introduces a “Personal Dead-reckoning” (PDR) navigation system for walking persons. The system is useful for monitoring the position of emergency responders inside buildings, where GPS is unavailable. The PDR system uses a six-axes Inertial Measurement Unit attached to the user's boot. The system's strength lies in the use of a technique known as Zero Velocity Update (ZUPT) that virtually eliminates the ill-effects of drift in the accelerometers. It works very well with different gaits, as well as on stairs, slopes, and generally on 3-dimensional terrain. The paper explains the PDR and presents extensive experimental results, which illustrate the utility and practicality of the system. Parts of this paper were presented at the 2006 International Joint Topical Meeting: “Sharing Solutions for Emergencies and Hazardous Environments,” February 12–15, 2006, Salt Lake City, Utah, USA.