At a plurality of first devices, wireless transmissions are received at different locations in a region where multiple target devices may be emitting. Identifier data associated with reception of emissions from target devices at multiple first devices is generated. Similar identifier data associated with received emissions at multiple first devices are grouped together into a cluster record that potentially represents the same target device detected by multiple first devices. Data is stored that represents a plurality of cluster records from identifier data associated with received emissions made over time by multiple first devices. The cluster records are analyzed over time to correlate detections of target devices across multiple first devices.