A Shenzhen-based company of 200 employees, Antebao develops and sells monitoring cameras, as well as anti-surveillance equipment and tracking devices. To demonstrate, He picks up a pager-like object with a thumb-sized, red-glass peephole in the middle and clips it to his phone, aligning the peephole with his phone’s camera. He flicks a switch, triggering red LED bulbs around the device’s peephole, and hands it to me.

“Go on,” he gestures, “see if you can spot the white dot.”

He explains that the red glass over the peephole filters out all other colour waves of light, so the screen on his phone will reveal a small, nearly imperceptible white dot on the everyday objects in the office, representing light refracted off the spheres of tiny camera lenses.

“What if I told you there’s a camera in the flower basket,” He asks, “would that make it easier?”

It does not. All I can see are everyday objects covered in a red layer. He takes the phone and points it at the basket, and tells me to focus my eyes, and then, there it is, between two flower petals, a small white dot, no bigger than a sesame seed.

We move on to the clock. I have to tilt it at an angle to avoid the glare from the glass face, but there it is again, a tiny hole drilled into the space above the loop of the number 6.

He casually flicks a fingernail against a water pipe running up the corner of a wall. “There’s one in here.” He points to the ceiling. “One up there. And one under the table, too.”

Spotting any of these cameras without such a device, forget about a second, third, fourth glance with the naked eye, is near impossible.

“No matter how you update spy cameras over the years, no matter how small they get,” he says, smiling slyly, his shorn round head and thin eyebrows giving him the look of a kung fu film antagonist, “the camera lens is a sphere, that doesn’t change – the lens will always be exposed.”

He’s desk sits opposite a wooden plaque, propped against the wall on top of a bookshelf. On it are a drawing of a ship and the words “Yi Fan Feng Shun” (“plain sailing”), scrawled in gold on a black background above a clunky digital clock. He says it belonged to a former client from five or so years ago, and this garish home decor is as good a place to begin his story as it is a souvenir.

A young couple was going through a divorce in Foshan, Guangdong province, and the husband knew the wife had evidence that he had cheated on her. So he decided to install spy cameras in their living room, hoping to catch her doing something, anything, that he could use as leverage in negotiations.

As it happened, the woman had anticipated her husband might do something like that, so she hired He, who travelled to the couple’s flat across the Pearl River Delta from Shenzhen, and proceeded to scan the room with his detection equipment. Sweeping past the lacquered “plain sailing” decoration, common back in the 1980s, He noticed the wiring for the clock left plenty of room for even a rudimentary spy cam to be hidden between the chunky number panels.

Bingo.

“When the woman saw the spy cam,” He says, “her face dropped.” It was shocking and hurtful that her husband would install such a device, but even so, she did not report her spouse’s surveillance to the police. Most clients, when they find out they are being watched, do not report it, says He.

Once, He says, he helped a businessman find a bug planted in his office, supposedly to steal business secrets. He suggested the businessman report the find to the police, but the man only said, “I know who it is,” and let it drop. Same with the Foshan couple, he says. People realise they “are still in the same circles and it will only get awkward”.

He had never seen a spy cam installed in such a place as the “plain sailing” clock, so when the job was done, he asked the woman if he could use it for training purposes. She agreed, and to this day, here it sits.

According to Chinese news reports, as early as the late 2000s portable spy cams were being used voyeuristically, as much by the pervert next door as paparazzi, and in women’s bathrooms as a low-budget substitute for pornography.

Cases from Japan and Hong Kong of women being “upskirted” had been reported for years, but in 2010, the Chinese public was shocked by news of a black-and-white video taken on an infrared camera showing Guo Jingjing, China’s “diving queen”, practising at a pool. In the 10-minute video, the infrared capture meant her genitals could be seen through her swimming suit.

As frightening a precedent as the Guo video was, most of the cameras back then were difficult to hide, and the video quality was shaky, pixelated, with no way to share the footage in real time. But by 2015, surveillance videos could be shot and shared via mobile phone, to say nothing of clandestine cameras the size of pinholes installed in all manner of appliances, with high-definition footage instantly uploadable to pretty much anywhere.

In 2005, at age 30, He Zhihui was discharged from the army and left his hometown of Tianmen, in Hubei province, hoping to make his mark in an already booming Shenzhen. That year marked the 25th anniversary of the city becoming a special economic zone, and roads were being rolled out like welcome mats to migrant workers keen to cash in.

But with little work experience, He was offered only low-paying jobs, such as security guard at residential compounds. Then one day, almost hidden in the folds of the Daily Sunshine and Southern Metropolis Daily newspapers, he read a few short advertisements for jobs at detective agencies claiming to “help you hunt down your debtors and find evidence of extramarital affairs”.

Intrigued, he called and scheduled appointments with a few, hoping his military reconnaissance skills might prove useful.

One particular firm stood out, located in the International Commercial Building, among the earliest skyscrapers in the city whose seemingly overnight construction had led to the term “Shenzhen speed” being coined. The agency seemed legit and well-to-do, complete with a receptionist’s desk and a 1,000 sq ft office for five staff. The industry was booming, the company head informed He, and they were looking to expand. They hired him on the spot, and he started work the next day.

The job was described as involving the occasional debt collection but mainly finding evidence of extramarital affairs – and most of the time, when wives suspected their husbands of infidelity, He says, their suspicions were well founded. He says husbands often suspected their wives, too, but he avoided those cases, believing that if suspicions were confirmed, the outraged husbands might harm the women.

At that time, there were about eight private agencies in Shenzhen, but private investigators all over the country were well connected on the instant messenger site QQ, and would meet up for dinner when passing through each other’s towns and talk about spying techniques and how to avoid trouble with the police.

The investigators knew they were operating in a legal grey area, even if criminal privacy law at the time consisted of just one line: “Those who steal or maintain a citizen’s personal information illegally could be sentenced for up to three years, and/or fined.”

With a fluid understanding of what information qualified as “personal”, investigators would conduct long interviews with potential clients to determine whether expected results would run afoul of the law. If there was reason to doubt the veracity of their claims, the company would request documentation, a marriage licence for example. And when working on a case, there were unspoken rules, red lines. Any photos of a suspect were to be taken in public, they all agreed, and there was no question of sneaking into people’s homes. That was a no-go area.

When tailing someone on foot, says He, it is best to do so from across the street: those being investigated, he says, are often suspicious and will constantly turn around to see if they are being followed. In pursuit by car, always stay a few lengths behind. Over the course of a case He would switch between two or three different cars, and “had several uniforms in the boot, like that of a delivery driver or a gas maintenance man, so I could switch identities constantly”.

But that is far from the whole story. If a husband met a woman for a meal, stresses He, that would not prove anything. If they held hands, still no. The detectives would have to wait until the couple under observation entered a hotel, then came out together the next morning, for example. Stake-outs could take all night just to get that one photo.

“It’s tough work,” he says, “not only risky, but it takes a toll on your body as well.”

He says he does not know the specifics of how these agents tapped private phone conversations – he just provided them with a phone number and they would give him typed-out transcripts of conversations associated with it.

One Shanghai lawyer who requested anonymity and has specialised in divorce and domestic affairs cases for 13 years says, in his experience, more clients use private detectives to find hidden assets than to prove infidelity. Tracking an affair takes a lot of time and energy but only proves the couple is breaking up, and will not provide leverage in terms of division of property in a divorce.

“You check someone’s credit status, there’s a lot of information, such as houses you registered, addresses, credit card info, mortgage,” he says.

For example: say a wife knows her husband is cheating and knows the other woman’s phone number but does not have evidence of where they are meeting or where the woman lives. The wife can hire a detective to find courier-service information linked to that phone, then track an address.

Then, “when the evidence is presented in court, they just have to say their spouse admitted it, or they found out. They don’t have to admit they found it through a private detective”, he says. “To the court, it’s normal for a wife to know her husband’s private life.”

In China, the sale of private information has become a common phenomenon. In 2017, state broadcaster CCTV aired an investigative report in which online “information vendors” provided an undercover reporter with an individual’s details, including property listing, phone conversations and even hotel check-in dates, all for a few hundred yuan.

As prevalent as infidelity seems to be, some cases do end up as false alarms. One female client said that every day her husband would go out in the morning and again in the afternoon, but came home for lunch and dinner. The couple owned two buildings and made sufficient earnings through rent that the man did not need a day job, and, therefore, had few reasons to be out every day.

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She thought he was having an affair, but then why would he and his mistress not eat together? He took the case and tailed the husband, only to find that he was visiting a KFC every day, staying for hours to look at stocks on his laptop, because his wife had forbidden him to do so at home.

Whether a suspect was caught being unfaithful, or the suspicions had turned out to be unfounded, He “started to feel that every time I completed an investigation, it ended in divorce. So I started thinking, ‘Was that the client’s purpose?’ It certainly wasn’t mine.”

Gradually – having felt increasingly guilty about his own success – He became something of a marriage counsellor while conducting investigations. When his clients would check in with him for updates, he would not only report his findings, but also provide advice on how to defuse tension and make progress through communication.

While working on one case, He says he observed the cheater in question arguing with his mistress on the side of a road at midnight. He reported this to the wife, telling her that despite the cheating, when the husband came home, not to pick a fight with him, but to talk to him with kindness, giving her examples of how to confront him without being too, well, confrontational.

With this new approach, He felt a sense of moral balance, but in 2009, a bigger problem presented itself when China updated its criminal law to include “workers at a government office or in finance, telecom­munications, transportation, education or medical facilities, who illegally obtain, sell or provide personal information”, declaring that offenders could be sentenced to up to three years, or fined. (When the criminal law was written in 1997, the most relevant clause it contained was about postmen opening, disregarding or destroying mail.)

The changes were “bound to have a large impact on our industry”, says He, “but we’ve formed our work habits over the years, and it was difficult to circumvent them all of a sudden.”

The Shanghai lawyer admits that cooperation with private detectives has decreased dramatically since 2009, those changes in the privacy law having made such cases more high-risk and sensitive.

In 2015, China tightened its grip on obtaining private information further, increasing the maximum sentence for leaking private information from three to seven years.

In a specific judiciary provision in 2017, after police had already cracked down on detective agencies, the Supreme Court elaborated on the clause, defining offenders as anyone who “illegally obtains, sells or provides more than 50 pieces of individuals’ travelling information, messages, or information about their credit scores and property”, or, more than 500 pieces of individuals’ “accommodation, messaging records, health and trade information”. Currently, offenders face up to seven years in prison and an unspecified fine for possession of such information.

In 2010, the Legal Daily, a newspaper run by the Communist Party’s Central Political and Legal Affairs Commission, reported on what it called the “first case of private detectives illegally obtaining individual information”.

Two detectives, Yuan Zheng and Yong Zhengde, were arrested by Beijing police in March of that year. They had similar backgrounds to He, taking on suspicious wives as their first clients, following the husbands, taking photos and recording conversations to provide proof of a marital indiscretion. They had a similar set of moral codes, too, such as keeping their clients’ information confidential and advising clients against seeking revenge.

“But their ‘moral codes’ were being spent in the wrong place,” the Legal Daily article declared, warning that if private detective companies were not shut down, the agents they employed would become criminals.

But those arrested were in Beijing, and in Shenzhen business went on as usual. Then on August 31, 2010, the dreaded day came: police arrived at He’s office for what they called a “routine check-up”. He later realised it was part of a nationwide clean-up effort – the police had researched every detective agency across China and were striking them down one by one.

They found five transcribed phone conversations on He’s computer, but “my first reaction was, that’s not that big of a deal”. In a lot of cases, a wife would request that He print out a phone conversation as evidence and he would get it from his usual black marketeers.

But he had underestimated the government’s determination to enforce the privacy laws: no one but the state was going to have that kind of spying power on its citizens.

He spent seven months in the Nanshan District Detention Centre awaiting trial. By the time his case was heard he had already served his time and was freed, but for the first three months of his detention he’d had a difficult time adjusting. He shared a 1,000 sq ft cell with about 60 other inmates, sleeping crammed together on the floor.

They wore drab, two-piece grey uniforms, and had a rigid schedule, calculated down to the minute. They all rose together, exercised in the yard, cleaned the cell several times a day and attended a required “study period” in the afternoon.

“Everybody here says they’ve been wronged,” one of his cellmates commented one day, “that they didn’t deserve this.” He decided to stop being just another whiner and to instead be productive. But, in contrast to the Hollywood cliché of a prison being a training ground for criminals, He’s “study period” was spent in a well-stocked library, poring over law books, in order to reimagine his business once he got out.

He spent the next few months reading up on criminal law, particularly the clauses that had got him arrested, and became familiar with what his skills would allow him to do legally. He could not keep spying on those unaware of his presence, but he could help clients who suspected they were being spied on.

Then, a Damascene flash in a Shenzhen detention centre: the more surreptitious the tech became, the more potential customers He could serve.

So he did the only thing he felt he could in the situation. He switched sides.

He began by setting up a stall at Huaqiangbei, with three childhood friends. The market has long been a hot spot for the latest tech trends, filled with shrewd businessmen sniffing out the most fashionable gadgets, shifting over the years from VCRs and telescopes to iPhone parts, bitcoin-mining equipment and, more recently, live-streaming classes for wannabe influencers.

Back in 2010, it was known for selling hardware components and small gadgets, and before the criminal law was updated, He had often visited Huaqiangbei for spy cams. Now reformed, he was on the lookout for spy-cam detectors. At the time, only crude devices were on offer, so he decided to develop a few prototypes, at a cost to him and his friends of 200,000 yuan (about US$30,000 at the time).

Liang Guangcai met He at the market. Liang had studied electronics in college and sold products he designed himself, mainly remote controls and tracking devices for cars. Liang found He professional and passionate. “He knew a great deal about the products and took his time with each test,” says Liang. “He was also patient with customers, and could go on explaining a product to them for hours.”

Liang and He became friends and discussed improving the products. In the beginning, they made modifications on detectors bought from Taiwan. “The radio frequencies in Taiwan and the mainland are different,” he says, “so we fine-tuned the detectors, otherwise they would have given false reports.”

As the business expanded, their products got smaller, easier to carry and more aesthetically appealing to female customers.

“My family didn’t know when I was working as a detective, and now they didn’t know I had moved into anti-spy investigations,” says He.

“I wasn’t making money and kept investing in new products. That’s a huge load of pressure on my family.”

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People walking by his Huaqiangbei stall were often intrigued and would ask about his products, but they seldom bought one. If anything, they wanted to buy the latest spy cams.

At first, the friend was selling only 100 shirts a day, at a profit of two or three yuan per shirt. But slowly, as China’s e-commerce system developed, the friend’s business increased to 900 shirts per day. It occurred to He that he could sell products through Taobao as well. Gradually, they were able to expand their target audience, and used feedback from customers all over the country to modify their devices. It wasn’t long before they started turning a profit.

This April, at Fukang Science and Technology Mansion, in a remote factory district of Shenzhen, amid the clattering of keyboards as Taobao technicians communicated with clients, I watched He prepare the day’s briefing about the latest spy-cam developments.

In the past, when a spy cam was installed in a plug socket, the socket was usually fake. But recently, a Taobao customer told them they had found a spy cam inside a real socket. Another client found one installed in the beam outlet of a television remote control.

“Remember,” He said to his assembled team, “spy cams are usually hidden where there are darker colours, or there’s a strange, tiny hole.”

He went over the basics of checking for spy cams in a hotel room: the air conditioner; corners of the ceiling; televisions; lamps.

If nothing else, he suggested, lie on the bed and look around. Such is the nature of hotel room spy cams – they are always pointed towards the bed.

These days, He handles the bigger gigs, such as sweeping for commercial clients, mostly companies concerned about industrial espionage, who have signed annual contracts with Antebao. Every quarter, their offices are swept for bugs, and before any large event, He walks into the venue, dons white gloves to prevent him from leaving fingerprints on any spying devices, opens up his suitcase and removes the tools of his trade.

In any one round of inspections, He says, he and his team use up to eight sets of equipment, including a spectrum analyser, analog signal capturer and magnetic wave detector. He scans the walls, computers, air conditioners, paintings, plants and under the furniture.

Each piece of equipment analyses some type of radio wave, and if any are abnormal, He locates where they are being emitted from.

Eighty per cent of the time, his inspections end with nothing, but the “client’s peace of mind is everything”.

In 2019, China saw the first lawsuit over the use of facial-recognition technology, after a professor in Hangzhou, Zhejiang province, sued a local wildlife park for replacing its fingerprint-based entry system with one that uses facial recognition – and won. The academic gained enormous online support with the public expressing anger over the zoo collecting people’s biometric data.

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In He’s cases, the spying equipment is mostly installed by people close to the clients.

Recently Antebao’s Taobao staff helped a woman in an on-and-off relationship. She had found it strange that her boyfriend seemed to know every aspect of her life, including what friends and relatives had visited her home. So she bought equipment from He’s Taobao store and inspected her flat with the aid of its staff.

She found a spy cam in a plug socket on the wall, and the Taobao technician suggested she should call the police. She chose not to.

Six months later, she found a new device in her air conditioner.

The government may have upgraded laws and cracked down on illegal spying, but people like that boyfriend will always exist and, therefore, He feels there will always be a need for his services.

“As the Chinese saying goes,” says He, “virtue is one foot tall, the devil 10 feet.”