It is nightfall in China's most watched city. Women nervously draw their curtains tightly shut, fretting that the cameras that record their daily trips to the office and shopping centre will pry into their homes and secretly film their most intimate moments.
Theirs is no hollow fear. Shenzhen is at the heart of a groundbreaking social experiment by the mainland government to monitor its vast population with the latest video and internet technology - and the boundaries of the experiment are for the first time being called into question.
In the past two years, more than 200,000 video cameras, many disguised as lighting columns, have been upgraded or set up from scratch along main streets, in shopping plazas and parks, and along highways in Shenzhen. The cameras beam live video to a central city database in a network that is well on its way to becoming the world's largest-scale use of technology for social control.
From the moment you step from Hong Kong into the city of 12 million, you are in range of hi-tech cameras, with a 360-degree scope, that look like miniature versions of the spaceships in the movie War of the Worlds.
Within two years, security analysts believe, Shenzhen will have video feeding into the database from as many as 2 million surveillance cameras - the highest concentration on the planet and four times as many as in London, the city whose model of protective watchfulness inspired the project. The experiment is part of a project across the mainland called Golden Shield, which is designed to tighten social control with the use of internet and video technology as security and anti-terrorism measures are stepped up ahead of the Beijing Olympic Games.
It might sound prohibitively expensive but the system has been implemented in an extraordinarily cost-effective manner. Private companies operating shopping centres, plazas and apartment blocks are asked to pay for the equipment then feed their video into the database, which is accessible by the police and government. The authorities, meanwhile, pay for the installation of surveillance cameras along highways and in public areas, pictures from which also feed into the database, making it increasingly possible to monitor an individual's movements step by step across the city.
In Shenzhen, according to deputy police chief Shen Shaobao, the experiment is already paying dividends. Crime rates have fallen by more than 10 per cent and police detection rates have risen by 2.6 per cent since the army of silent sentries first went on duty in 2006. Criminals are increasingly aware they are being watched and are less likely to strike in public.
'Everyone knows they're being watched now,' a 30-year-old hawker says, glancing up at one of the cameras outside the Lowu Commercial City shopping plaza, immediately over the border.
'No one even dares sell a [pirated] DVD here any more unless they're behind the shutters of a shop because the cameras see everything.'
It seems the public aren't necessarily unhappy with the situation. The satisfaction rating of citizens towards the public-order situation in Shenzhen - once one of the most crime-ridden cities on the mainland, thanks to a volatile migrant population - went up 17 per cent year on year to 87.5 per cent last year, according to police studies. Shen is understandably delighted at having been able to achieve such dramatic results in a relatively short time.
'We used London's financing model to get society and corporations to pay for the cameras while we unified the technology,' he said last year. 'Within one year we established a surveillance system with 200,000 closed-circuit television [CCTV] cameras across the city. We accomplished a mission impossible.'
In a country where social control is rarely questioned, the sudden appearance of lamp-post-style security cameras across the city had not been seriously challenged - until a few months ago, when a seemingly trivial sequence of events made the city's residents aware that technology can be a double-edged sword.
Residents at the Wang Ye Gardens apartment block, just 3.2km from the Hong Kong border, noticed that a rooftop surveillance camera on a neighbouring building supposedly monitoring traffic swivelled around at midnight every day and trained its high-powered lens on their windows until 5am. A local newspaper journalist alerted by residents watched the camera for a fortnight and - by monitoring a government website where CCTV footage from cameras across the city was made available - saw it was being used to scan the apartment block for lit windows and film women in their bedrooms and bathrooms.
The story broke in mid-May, with grainy photographs of naked women getting in and out of baths and walking in front of bedroom windows splashed across the front page of popular Shenzhen newspaper Southern Metropolis Daily. It was a story that almost caused a riot.
'People were very, very angry about it,' says a spokesman for the apartment block's management company. 'When the pictures were first published in the newspaper, some of them wanted to go out and smash all the CCTV cameras. They just didn't want them there any more, but what could we do? We had to tell them, 'They are government property and we can't move them.''
The events at Wang Ye Gardens have served as a wake-up call to the extent to which public surveillance has developed in Shenzhen. 'It is like being under the watch of Big Brother from [the book] 1984,' says Li Xiang, a middle-aged man living on the estate and one of the few willing to talk about the scandal. 'After this incident, I realised that as soon as you step out of your door in this city, you are under CCTV surveillance.
'You are watched at every crossroads, in every train station, on every street and every escalator. Even when you get on a bus, there are CCTV cameras taking a picture of everyone's face as they get on board.' Some people are asking how long it will be before taxis are fitted with surveillance cameras.
It is not only residents of Wang Ye Gardens who are concerned about the pervasive use of CCTV. In a country where political activists face jail for opposing the Communist Party and where a variety of political and spiritual groups are closely monitored, human rights groups fear the technology will soon be used to identify and arrest democrats and dissidents.
'Activists used to just be tailed by secret-police agents when they met up in Shenzhen,' says one Hong Kong-based activist who meets regularly with underground labour-rights groups on the mainland. 'Now they are concerned that as well as the police, they will be followed everywhere by CCTV cameras - and those cameras will be much more efficient than the police agents.
'It puts psychological pressure on activists as well as increasing their risk of being arrested.
They may not have face-recognition technology on these CCTV cameras yet but they can easily be upgraded when the technology is available and no one will know.'
What is certain is that the surveillance industry is becoming big business on the mainland. Companies working in the sector made US$500 million in 2003. The trade association representing them has seen so much growth that it expects the sector to be worth US$43.1 billion a year by 2010.
Whereas a little over two years ago, surveillance cameras were operated independently by government bodies or private companies in different parts of the city, the central database represents a quantum leap in terms of how the information the cameras generate can be used. One of the most significant steps in the project came in 2006, when the government ordered that all internet cafes install video cameras with a direct feed to their local police station - a stipulation intended for 660 towns and cities across the mainland, but implemented first and most effectively in Shenzhen.
Banks of video screens line the walls of police stations in Shenzhen, showing real-time images from points across the city centre and keeping people's movements under constant watch.
The Golden Shield project extends beyond CCTV. According to the blueprints, phone calls will be monitored by digital voice-recognition systems, internet access tracked and an ID-card scheme set up that will eventually provide a national database featuring the photograph of every one of the mainland's 1.3 billion citizens (again, Shenzhen is the guinea pig; from August 1, every migrant worker in the city must enrol for a hi-tech residency card). And the technology may be at a more advanced stage than even the dissident groups realise.
According to Xue Junling, a project manager with Shenzhen Xinhuo Electronic Engineering, which set up 38 surveillance cameras around the city's Civic Centre, person-recognition technology is already being widely used in Shenzhen. The technology enables the irises, facial features and even the gait of subjects under view to be checked electronically against a database of people the police or government security services wish to monitor.
'We already use face-recognition technology in government offices and in the entrances to shopping malls in Shenzhen,' says Xue, clearly excited by the possibilities of the technology. 'It doesn't matter how far away from the subject your camera is. If you have a good lens you can zoom in and do face-recognition.
'The technology is being upgraded day by day and the connectivity of the different parts of the system to a central monitoring desk is also being constantly improved. Surveillance of this kind is a nationwide movement in China. Even small towns are trying to build up their systems, even though they don't have the resources that we have here.'
For Xue, there is nothing sinister about the use of surveillance. With disarming frankness, he says: 'We are also doing mobile surveillance during the Olympics for the Ministry of State Security. We have surveillance equipment inside a plain vehicle. We park it at Olympics venues and it sends data and pictures by satellites to the ministry.'
A mainland-based human rights activist, who asked not to be named for her own safety, says: 'We're worried the government is using the Olympics as an excuse to import this technology from western companies. Then when the games are over, they will use that technology to identify and round up dissidents.'
Gazing out across the sprawling Shenzhen cityscape from his 25th-floor office, Xue, whose company has grown wealthy from the city's surveillance boom, sees no such dark clouds on the horizon. 'We are the national leaders in this type of technology. We are the city of peace, harmony and security,' he says with pride.
For the residents of Wang Ye Gardens, Shenzhen is also the city of unwarranted intrusion. Embarrassed by last month's revelations, the city government reacted by ordering the sacking of the two operators who spied on the women - then blocked public access to the government website showing the CCTV footage.
'It isn't good enough,' Professor He Bin of the China University of Political Science and Law in Beijing complained to one Shenzhen newspaper. 'Why didn't the government disclose the names of the people responsible and reveal the full details of the case? People have a right to know this information otherwise more people will be harassed in the future.'
As far as human rights groups are concerned, that harassment could manifest itself in far more sinister and liberty-threatening ways than the grainy footage of women stripping off in Shenzhen's crowded apartment blocks.