There is growing uncertainty over the use of smart glasses in public and the nefarious ways they could be used to violate the privacy of everyday people.

Sally Contarino, a 26-year-old Australian tourist, was secretly filmed outside a Las Vegas 7-Eleven by a man wearing Meta smart glasses, who approached her with a pickup line while the tiny camera built into the frames captured their interaction.

The footage took on a much more disturbing significance days later, when Contarino disappeared during her solo trip to Las Vegas. The recording became one of the last known videos of her before she vanished.

Another BBC investigation in January highlighted just how easily people can be filmed without their knowledge.

Dilara, a 21-year-old shop assistant, was on her lunch break when a man approached her and began flirting with her. What she did not realize was that he was wearing Ray-Ban Meta smart glasses and secretly recording their interaction.

The footage was later posted to TikTok, where it amassed more than 1.3 million views. Her phone number was also visible in the video, she said, leaving her bombarded with texts, calls and FaceTime requests from strangers.

Now, one software developer has created an app that claims to offer a way for people to detect nearby smart glasses – and even estimate how far away they are.

Pawel Szydlowski, 30, said that the idea was born from his own fears after watching videos of people using smart glasses to not only record but identify unsuspecting strangers.

That led him to launch Zuckoff, which has already garnered 5,000 users since its launch on Apple's App Store last month.

The app functions like a map, showing users the likely proximity of nearby smart glasses.

Szydlowski said he began by obtaining various models of smart glasses and examining the Bluetooth signals they broadcast to determine their Bluetooth 'fingerprint.'

Those broadcasts can include universally unique identifiers, or UUIDs, which identify specific Bluetooth services supported by a device. Some devices have Bluetooth services actually called 'Meta' or 'Ray-Bans,' Szydlowski said.

The Zuckoff app compares several pieces of information broadcast by a device, including its UUID and manufacturer identifier, to determine whether it matches a known pair of smart glasses.

'If the unique identifier matches, and also if the manufacturer identifier matches, then we have like an ultimate combo there,' he said.

The paid version, called Zuckoff Pro, sends notifications when recording-capable smart glasses are nearby, even when the app isn't open. It costs $24.99 as a one-time payment and does not renew.

Users can also opt for a yearly subscription, which costs $9.99 a year, with the first year free.

The app targets Ray-Ban Meta and Oakley Meta glasses, Snap Spectacles, display glasses and headsets such as the Quest and Vision Pro.

It comes as Meta faces mounting criticism over how the technology can be used, prompting the company to launch a PR blitz aimed at soothing privacy fears.

This month, Meta bricked thousands of glasses after discovering that the built-in LED lights, which are designed to turn on automatically during recording, had been tampered with.

Despite the criticism, top executives at the company have repeatedly emphasized that the glasses are designed to be safe. In one Instagram video, Meta Chief Technology Officer Andrew Bosworth said: 'We designed this camera to be noticed by the people around you.'

But that assumption is precisely what concerns Szydlowski.

He grew up during the YouTube era, when prank videos were all the rage. But there was a crucial difference: if someone clearly didn't want to be recorded, many creators blurred their faces. And the majority of pranked pedestrians were aware of the camera being thrust in their face.

Smart glasses changed that dynamic.

Pickup artists still filmed themselves practicing their skills on women, Szydlowski said, but now the women being filmed could not always tell they were on camera.

What's more, Szydlowski noticed that obviously uncomfortable subjects were rarely having their faces blurred in the videos he saw. When he checked the comments, he said he saw users doxxing the people featured in them.

'With this type of content, I've seen a lot of emotions in me,' he told Business Insider.

For Szydlowski, the solution was relatively simple. If tech companies were not going to ensure that their glasses were clearly recording, he was going to give people a way to know for sure when one was nearby.

'We as a society have the right to at least know that someone is recording,' he said.

Szydlowski said Meta could take a page from Apple and Google's response to concerns that AirTags and other Bluetooth trackers could be used to secretly track people.

The two companies developed an industry standard that allows iPhones and Android devices to warn users when an unknown Bluetooth tracker appears to be traveling with them.

Smart-glasses makers could adopt a similar system, Szydlowski said, allowing people's phones to alert them when the devices are nearby.

'If they really care about that part not being abused, they would go that way,' he said.