A new surveillance system called SignalTrace, marketed by security firm Leonardo, links automatic licence plate readers with sensors that detect nearby electronic devices such as phones and smartwatches. By logging which devices repeatedly travel together with a particular vehicle, the system builds "electronic signatures" that can later be searched even without knowing a car's number plate, allowing investigators to trace a person's movements and associations before establishing their identity. Leonardo maintains the technology "does not identify people" since it only captures device signals rather than names, but researchers argue this is a narrow definition, as repeated links to a registered vehicle, a home address, or another known device can effectively reveal who was carrying it.

The system reportedly works by pairing licence plate camera data with detected Bluetooth or radio frequency signals, storing these fingerprints for later police queries. Leonardo's own product materials describe the technology as helping "identify suspects" through the mix of devices they carry, and an associated patent refers to tracking "targets" — people or vehicles — by correlating searchable signatures with visual identifiers across locations. According to the article, devices using the system, or its predecessor, have reportedly been installed in Oxon Hill, Maryland, and featured on an official New York state contract price list, though it is described as a tested and marketed capability rather than yet being widespread police practice.