A presence detection system (100) including: an RFID interrogator (102); and a plurality of passive RFID tags (11 to MN), the RFID interrogator (102) is configured to: measure a received signal strength indicator (RSSI) level from each of the plurality of passive RFID tags (11 to MN); compare a measured RSSI level to a reference RSSI level for each of the plurality of passive RFID tags (11 to MN); and determine whether a difference between the measured RSSI level and the reference RSSI level is greater than a threshold value.