The study, presented at the USENIX Symposium on Usable Privacy and Security (SOUPS), evaluated 19 widely available detectors using participants from a range of backgrounds to search for surveillance devices hidden in mock living rooms. The participants found the detectors were often difficult to operate and hard to interpret. As a result, they missed finding nearly 60% of hidden surveillance devices – only a slight improvement over participants using just their own eyes to search.
Commercial surveillance devices
In recent years, a growing range of disguised surveillance devices has become commercially available through manufacturers and mainstream online marketplaces, with few restrictions on their sale. These include cameras, microphones, and GPS trackers concealed within everyday items such as clocks, USB chargers, smoke alarms, picture frames, and plush toys.
Although these devices are often marketed for personal security or other types of home protection, they can be misused by malicious individuals. This often includes domestic abusers who use them to secretly spy on intimate partners, a form of technology-facilitated abuse often linked to coercive control, financial abuse, and physical violence.
This has fuelled a parallel market of consumer detectors that claim to identify hidden surveillance equipment. However, many of these products present users with signal-strength readings, technical terminology, and radio-frequency measurements that requires specialist knowledge to understand, making them difficult for typical consumers to interpret correctly.
To assess their real-world effectiveness, the researchers had 34 participants search for hidden surveillance devices in simulated living rooms containing furniture, home electronics and other common household items. They found that the detectors offered only a modest improvement: participants using a detector still missed 58.8% of the surveillance devices, compared with 66.7% when searching without one.
However, one category of tools performed substantially better than the rest. Smartphone apps designed to detect Bluetooth trackers, including Apple AirTags, missed only 27.6% of devices and produced no false positives. Rather than simply detecting wireless signals, these apps presented users with recognisable devices they could investigate, helping them understand what had been detected, verify whether it was suspicious, and decide what to do next. While Bluetooth trackers represent only one method of hidden surveillance, they are one of the most commonly used by abusers.
Lead author Akhil Polamarasetty, a Ph.D student at the UCL Centre for Doctoral Training in Cybersecurity, part of UCL Computer Science, said: "Searching for hidden surveillance devices is challenging both technically and emotionally. Most of the detectors on the market are not designed with the typical consumer in mind. Many people do not necessarily understand the limitations of such detectors and risk misinterpreting the results. Our research found that the difference between the best-performing tools and the rest of the market wasn't simply their ability to detect signals—it was whether they helped people understand what those signals actually meant. So the crucial difference is usability. If products are intended to improve people's safety, they need to be designed around what a typical user actually needs.”
The emotional cost of confusing tools
The researchers found that poorly designed detectors carried emotional as well as practical consequences. For survivors of domestic abuse, who often already live with heightened vigilance and self-doubt, missed surveillance devices can leave them at continued risk, while false positives may trigger unnecessary anxiety.
When a detector incorrectly flagged an ordinary object as suspicious, participants sometimes became trapped in anxiety spirals, repeatedly searching the same area without finding an explanation. Conversely, when a detector failed to identify a genuine surveillance device, participants often assumed a room was safe when it was not, creating a potentially dangerous false sense of security.
Drawing on these findings, the researchers developed a new framework for evaluating hidden-device detectors that includes their usability, interpretability, verification support and emotional safety in addition to their technical detection accuracy.
They also proposed recommendations for manufacturers, including providing clearer guidance, presenting detected devices in ways users can understand, communicating uncertainty more effectively, supporting verification rather than simply detection, and considering the emotional impact of product design.
However, the researchers added that even with their recommendations, no detector would likely ever be perfect. They emphasised that the only way to prevent this kind of technology-facilitated abuse is to stop the sale of hidden spy devices entirely.
Senior author Dr Leonie Tanczer (UCL Computer Science) said: "Most technology is dual-use, and companies have a responsibility to think about how their products can be misused at the design stage rather than after the harms emerge.
“At the same time, we also need greater scrutiny of the growing market for covert surveillance devices themselves. Many of the miniature surveillance devices we examined are sold as ordinary consumer security products, yet their defining feature is concealment, because the only reason to build a camera into a USB charger or a digital clock is so that nobody knows it is there. The people most at risk are paying the cost of a market that continues to normalise products designed for covert surveillance."