License plate readers can now track your phone too, thanks to new surveillance tech

License plate readers are now being used to track smartphones, thanks to a new surveillance technology called SignalTrace. Developed by the security company Leonardo, this system can identify groups of consumer devices that move together regularly and associate them with vehicle records and locations.

For example, if the same phone signal is seen near a car connected to an investigation, investigators can use the previous association with a known vehicle to work out who was carrying the device. While the signal itself may not contain a person's name, its link to a known vehicle can provide investigators with another clue.

SignalTrace works alongside automatic license plate readers, allowing investigators to search for patterns even when they don't know the license plate number in question. The system's creators emphasize that it does not identify people directly, but rather collects electronic signatures from signals already being broadcast by devices like smartphones and smartwatches.

However, this data can still be used to identify individuals indirectly by linking the patterns of movement to other records. For instance, if a person's phone signal repeatedly appears near a specific car that is registered to someone else, investigators may be able to infer a connection between the two.

While SignalTrace itself does not reveal a person's identity, the potential for linking movement patterns to existing records raises concerns about privacy and the extent of Fourth Amendment protections. Courts have recognized that phone location records can reveal significant personal information, and there is a risk that SignalTrace could be used to track individuals' movements and associations even when their identities are initially unknown.