Abstract: An indoor location system has acoustic wave emitters, electromagnetic emitters, and a mobile device. Each acoustic wave emitter is configured to emit an acoustic wave having an acoustic wave frequency and wavelength, and an electromagnetic signal that includes electromagnetic emitter data related to that electromagnetic emitter and data indicative of a frequency and/or wavelength of an acoustic wave emitted by the acoustic wave emitter that is associated with that electromagnetic emitter.

Abstract: A location system with an RFID tag, first and second location receivers and a central server receiving information from at least one of the first and second location receivers. The system calculates the RFID tag's location. The system may include a short-range exciter. The short-range exciter transmits a low frequency signal, possibly at 125 kHz. The central server creates a record containing information when the multiple RFID tags were within close proximity. The RFID tags can provide an indication that they were within close proximity to each other, via audio signals and/or haptic vibrations.