Think Flock is bad? This new tech is coming to link license plates with your phone — and it could be another death knell for privacy

Flock is continuing to face public ire over the ways that its national network of license plate readers can be used and abused in the US, but there's bad news for anyone worried about their personal privacy and widespread surveillance: technology that's even more concerning is on the way.

That tech is SignalTrace from security company Leonardo, a system that takes the license plate reading approach of Flock and raises the sophistication a notch.

SignalTrace scanners can identify the types of devices that are in a car as it passes by, and link them to a person even if the license plate number isn't visible.

So, for example, a car of interest to the police might have an iPhone, an Audi stereo, and a pair of Bose headphones in it.

The next time that specific combination of devices is detected on the SignalTrace network, an alert can be sent to law enforcement.

While the technology hasn't yet been broadly deployed, security researchers are already asking questions about the potential implications and the possibility of innocent members of the public getting caught up in investigations.

Here's how the technology works and what might happen next.

How SignalTrace works Virtually every electronic device you use is broadcasting some kind of Bluetooth or Wi-Fi information.

It's how your phone stays connected to cell towers, how your fitness tracker syncs stats back to the web, and so on.

SignalTrace scanners work in addition to license plate reader cameras to catch these signals and interpret them.

Over time, the system sifts through combinations of these devices (which will typically include some of the electronics in your car too), to figure out which gadgets regularly travel in a vehicle together, suggesting the same people are inside.

That gives law enforcement a way to monitor where a vehicle is and when over time, and more information about who is actually in the vehicle too.

"Algorithms can determine which specific mix of devices are predictably moving together," explains Leonardo on its website .

"That specific mix of devices — linked by common time stamps and locations — are described as an electronic fingerprint and can help develop leads that aid investigations." SignalTrace readings can be used with other data (Image credit: Leonardo) It's a little bit like the browser fingerprinting techniques that websites use.