A locator beacon, method and system for identifying a first-in-line device, including: a first antenna configured to send a first signal; a second antenna configured to send a second signal and spaced apart from the first antenna such that a delta value between a first Received Signal Strength Indicator (RSSI) value of the first signal and a second RSSI value of the second signal measured at a predefined location, is within a range of values; a receiver for receiving wireless signals configured to receive an authentication signal from a mobile device adapted to measure the first and second RSSI values, the authentication signal including authentication data related to the measured RSSI values; and a processing unit, configured to determine whether the mobile device is the first-in-line device based on whether a delta value between the first RSSI value and the second RSSI value is within a predefined value range.