Abstract: An indoor location system for locating a mobile device has at least one mobile device configured to be a radio frequency receiver or beacon signal transmitter, and a set of radio frequency units configured to be positioned in a plurality of rooms in a building. One or more of the radio frequency units is located in each room, and each unit is configured to emit or receive radio frequency beacon signals. The mobile device, or each radio frequency unit, is configured to determine a received signal strength (RSS) of each of the received beacon signals. The mobile device, or a computer module connected to the radio frequency units, is configured to calculate from the RSS a room-representative RSS for each room, and to determine which room the mobile device is located in, by selecting the room having the highest value of calculated room-representative RSS.