The watch’s insecurity and the spying it enabled might be expected given the gadget’s pedigree: It’s sold by an obscure company called CJC, costs less than $30, and was made by an equally obscure manufacturer, YiQingTeng Electronics, in Shenzhen, China. More troubling, perhaps, is that the online platform it’s built on—and the one that allowed Stykas and Solferini to so thoroughly hack it—is used by dozens of other brands of smartwatch, many of which have likely been left vulnerable to the same forms of digital stalking.

At the Black Hat cybersecurity conference today, Stykas and Solferini plan to present their findings from analyzing the supply chain and security of more than 70 GPS-enabled watches and car accessories. They found that more than 30 of those geolocation devices use the technology and backend servers of YiQingTeng, also identified by the brand name Wonlex, the name of a partner firm Shenzhen 3G Electronics, or their associated app, SETracker. Another 30-plus brands of tracking devices for cars and kids are all run on another Shenzhen-based platform known as NewGPS2012.

Combined with another major GPS platform known as SinoTrack that sells car trackers and smartwatches, the two researchers found that tens of millions of GPS tracker gadgets came from just three supply chains. All three, the researchers found in their analysis, had significant security flaws—in some cases as simple as a lack of authentication that allowed anyone to access any device—leaving children’s watches vulnerable to tracking by a hacker, location disabling and spoofing, interception and spoofing of text and audio messages sent to them, replacement of emergency contacts with ones a hacker chose, silent audio eavesdropping, as well as photo and video capture for camera-enabled devices. (Once the GPS started working on the smartwatch WIRED tested, the hackers showed that feature, too, could be hijacked to follow the wearer’s every move.)

For some GPS-enabled car accessories, the researchers found they could similarly track the devices’ locations or spoof messages to them that could potentially unlock or disable cars, though the researchers didn’t go so far as to test this out on actual vehicles. They also say they found server-side vulnerabilities that exposed consumer information, would have allowed them to execute their own code on the servers, or even in one case appeared to show that someone else had already gained unauthorized access to the system’s backend.

“Millions of kids are being exposed and vulnerable to exploitation. It’s just catastrophic. It’s really low-hanging fruit for a lot of bad actors,” Stykas says. “Your criminal mind is the only limitation in exploiting those devices.”

The Watches Watching Your Kids

The researchers say they’ve been warning the companies behind all three Shenzhen-based GPS platforms about their vulnerabilities for months. When WIRED reached a representative of SETracker, the person initially claimed in an email that “the issues you mentioned have been resolved long before,” adding that “we attach great importance to the security of Setracker and keep strengthening its security continuously.” When WIRED pointed out that researchers had been able to hack a smartwatch running on SETracker just this week, the person repeated their claim that the issues had been fixed, then asked for evidence of the exploitation, which WIRED provided.

Only today, hours before the researchers’ talk at Black Hat, did the researchers find that their hacking techniques against SETracker’s platform have stopped working—though they’re still not sure if the flaws they found are fully fixed.

Sinotrack and the NewGPS2012 platform didn’t respond to WIRED’s requests for comment, and the researchers say their hacking techniques against those systems still appear to work.

For more than a decade, cybersecurity experts and privacy advocates have warned that cheap, GPS-enabled children’s smartwatches and aftermarket vehicle accessories are riddled with security vulnerabilities that leave kids and drivers susceptible to hacking and tracking. But the sheer number of different brands and models of those devices has often made identifying the truly insecure gadgets feel nearly impossible for consumers.