Systems (100) and methods for determining a location of a tag (310). The methods involve: receiving, at each detector of a plurality of detectors (202-216, 306, 308), a device transmission periodically transmitted from the tag; determining, by the detectors, Received Signal Strength Indictors (“RSSIs”) for the device transmission received thereat; determining, by a computing device (218), a probable location of the tag within the passage, first demarcated area or second demarcated area using the RSSIs and relationships between the RSSIs; determining a first likelihood value indicating the likelihood that the probable location is correct; and determining an estimated location of the tag within the passage, first demarcated area or second demarcated area based on the probable location when the first likelihood value meets a first criteria.