A detector, positioned at a first geographic location, receives a message from a mobile device that is sent without a request from the detector and via a short-range communications protocol, such as Bluetooth® or other WPAN. The detector parses the message to obtain data associated with the mobile device, such as extracting a media access control (MAC) address, a device type, or other information from the message. The detector may further identify an attribute, such as a signal power loss or frequency, associated with the received message. A second geographic location, associated with the mobile device, may be determined based on the attribute. The detector may also identify an associated user based on the data associated with the mobile device. The local device may receive data identifying, for example, the user, the second geographic location, or preference data related to user.