An access control system for monitoring a public access point, comprising: a positioning unit for tracking locations of users carrying smart phone user devices relative to the public access point based on wireless signals from the smart phone user devices, wherein the positioning unit comprises a directional antenna (111-b) for establishing close proximity of the smart phone user devices to the public access point, wherein the directional antenna is orientated downwards, and an omnidirectional antenna (111-a) for receiving the wireless signals and continuously monitoring the smart phone user devices, wherein the positioning unit is installed above the public access point, and wherein the positioning unit determines whether the smart phone user devices are within a threshold area of the public access point by comparing signal strength of wireless signals received by the directional antenna with the signal strength of the wireless signals received by the omnidirectional antenna, including inferring that the smart phone user devices are within the threshold area of the public access point when each of the antennas receive wireless signals from the same smart phone user device with a high signal strength as compared to expected values, inferring that the smart phone user devices are within the threshold area of the public access point when each of the antennas receive wireless signals from the same smart phone user device that are relatively the same in strength but each have a very low or weak value for their signal strength, and inferring that the smart phone user devices are not within the threshold area of the public access point when the directional antenna receives a relatively weak signal or no signal and the omnidirectional antenna receives a signal with a nominal strength compared to expected values; wherein the access control system is configured to determine whether the users are authorized to pass through the public access point based on the wireless signals from the smart phone user devices and provide access through the public access point for the authorized users when the authorized users are determined to be within the threshold area of the public access point. a positioning unit for tracking locations of users carrying smart phone user devices relative to the public access point based on wireless signals from the smart phone user devices, wherein the positioning unit comprises a directional antenna (111-b) for establishing close proximity of the smart phone user devices to the public access point, wherein the directional antenna is orientated downwards, and an omnidirectional antenna (111-a) for receiving the wireless signals and continuously monitoring the smart phone user devices, wherein the positioning unit is installed above the public access point, and wherein the positioning unit determines whether the smart phone user devices are within a threshold area of the public access point by comparing signal strength of wireless signals received by the directional antenna with the signal strength of the wireless signals received by the omnidirectional antenna, including inferring that the smart phone user devices are within the threshold area of the public access point when each of the antennas receive wireless signals from the same smart phone user device with a high signal strength as compared to expected values, inferring that the smart phone user devices are within the threshold area of the public access point when each of the antennas receive wireless signals from the same smart phone user device that are relatively the same in strength but each have a very low or weak value for their signal strength, and inferring that the smart phone user devices are not within the threshold area of the public access point when the directional antenna receives a relatively weak signal or no signal and the omnidirectional antenna receives a signal with a nominal strength compared to expected values; wherein the access control system is configured to determine whether the users are authorized to pass through the public access point based on the wireless signals from the smart phone user devices and provide access through the public access point for the authorized users when the authorized users are determined to be within the threshold area of the public access point.