An approach is provided that receives, from a radio frequency identification (RFID) tag included with a device, at least three different charge times. Each of the charge times corresponds to a different RFID reader that separately charges the RFID tag with each of the RFID readers being at a different geographic location. A distance between each of the RFID readers and the RFID tag is approximated based on the respective charge times and these approximate distances are used to identify a geographic position of the RFID tag using trilateration. The geographic position of the RFID tag is then used to determine whether to allow the device wireless access to a computer network.