Indoor localization by wireless technology (e.g., GPS and cellular-based localization) remains problematic despite many years of research due to the impairments the building structure creates for wireless propagation. While there are niche wireless technologies (e.g., UWB, some RFID, Wi-Fi fingerprinting) suited to indoor use, they require that building occupants carry some device to enable localization. A new invention provides sub-meter localization accuracy without imposing any requirements on building occupants. With a novel application of decades old building sensor instrumentation technology, the invention can detect and locate a person from their footstep-generated floor vibrations. The invention accounts for the subtle, non-obvious interaction of the footstep-generated vibration with the building's structure to provide localization accuracy that is otherwise infeasible with conventional localization algorithms.