A pinhole video briefcase, a secret camera hidden in a cigarette box and a recording device in a pen are just a few of the special tools tailor-made for private detective Kelvin Ko when he and his staff of 80 investigate a case.
Mr Ko, a former policeman, became a private detective eight years ago. Then, two years ago, he co-founded the detective agency Intellect Consultancy.
He is a specialist in commercial due diligence - conducting background checks on potential partners, cracking down on fake products and intellectual property rights infringements and investigating commercial disputes.
But the most interesting part of his business may well be matrimonial investigations.
'In nine out of 10 cases, the suspicion is proven to be true,' Mr Ko says. 'And it is not always the wife checking on the husband. We have an equal number of cases in which the husband wants the wife investigated. Interestingly, about only 30 per cent of the time it is a homosexual affair that we discover when we trace the targets to a gay or lesbian bar.'
The cases usually end in divorce.
'When a client wants the private detective to become involved in their marriage, there is no trust,' he says. 'We are there to help them collect evidence for the divorce, separate their assets and determine custody of their children. It is very sad.'
Mr Ko recalls the case of an old woman who suspected her 75-year-old husband was spending HK$2,000 three times a week on prostitutes. The investigation showed she was right, and she wanted the detective to continue following her husband to the point that she was spending more money on surveillance than he was on call girls. 'I had to say no to her,' he says.
'I encouraged her to go back to the US alone to enjoy her life as grandmother, instead of wasting more money. Ethics is a golden rule of a professional investigator.'
Some cases have happier endings. A wife once hired him to follow her spouse's mistress and collect evidence to show that the other woman had many boyfriends other than her husband. She then successful convinced her husband to end the illicit relationship.
For surveillance, Mr Ko will typically charge about HK$1,200 per hour, though some project-based cases could cost HK$10,000 to HK$2 million.
These fees brought a turnover of about HK$25 million last year for the company set up by Mr Ko and his three partners - all former officers. They have former policemen and policewomen on their staff.
'It is necessary to have someone who has investigative training,' he says. 'Sometimes we have to follow our targets. And sometimes we have to go undercover at a factory or other company we are investigating. These valuable skills are not taught in any college but only in the police force.'
What makes his life different from his years in the police force is that he doesn't report to anyone except the client, there are fewer restrictions on his work, and he can choose the cases he likes.
The result can sometimes be the same - an investigation may lead to a report to customs officials, the police or the Independent Commission Against Corruption for further action.
So why don't customers go free of charge to the police from day one?
'First, they want to keep a low profile and not wash their dirty linen in public,' he says. 'They want to find out if their suspicions are correct, without going through legal channels. For example, they may prefer to fire a wayward employee, whereas the police may insist on pressing charges.
'Secondly, there are some cases where it is not clear that a law has been broken and yet the client wants to collect evidence.'
There is no shortage of clients, but the nature of the investigations can change with the economic cycle.
'Before 1997, many companies hired us to check on prospective employees to see if they had stolen from their clients,' Mr Ko says.
'After the 1997 Asian financial crisis, banks hired us to identify borrowers who went into hiding. During the 2000 dot-com bubble, companies wanted to check if anyone had stolen their IT concepts. Recently, people want information about their mainland business partners.'