All cars are checked and identified. If they appear suspicious they are followed. A further group patrols the streets. It is supplied with two-way radios bought with money raised by the villagers.
It was revealed last week that people in Wigan, Lancashire, had paid for security patrols to guard their properties. Here in the south Wales valleys, where unemployment runs at 20 per cent, they provide their own protection.
The action group - the word 'vigilante' is disliked - was formed last November when a spate of crime brought complaints that there were not enough policemen on the beat.
One night alone, five cars were stolen. On average, five crimes - break-ins, vandalism and muggings - were being reported each weekend. More than 100 people turned up when the scheme for mounting patrols was first suggested.
After a cabaret night at the village social club, volunteers for that night's patrol met near the old police station, built in 1907 and closed 15 years ago. The patrols are unarmed - their intention is to observe and call the police if necessary.
Rumours that they carried baseball bats led to the police searching their cars. Nothing was found. But Colin Day, the action group chairman, said: 'We have some handy lads out at night. Many are ex-miners. They can look after themselves'.
They need to. Patrol members have faced increasing abuse from certain residents of a recently- built housing estate. Cars have been vandalised, families threatened and stones thrown.
Wayne Lewis, 26, a roofer and founder-member of the patrols, had his car rammed while it was parked outside his house. He was also attacked by a gang carrying sticks. 'I'm not going to be beaten,' he said.
His neighbour, Paul Mizen, 35, who works in insurance, said his family received abuse every day but it had not deterred him. 'It is frustrating because we know who is responsible. We would all rather be at home with our wives, but we have to do something positive to tackle crime.'
Mr Lewis said that there was support from the police on the ground. The patrol had been successful in bringing some criminals to book and officers had asked them to watch out for stolen vehicles. But officially, police support is more cautious.
Senior officers addressed a public meeting in the village and warned locals they should not take the law into their own hands. South Wales police said: 'We press them to form a Neighbourhood Watch. If they are about in the evening and see anything they should report it to the police.'
There is a strong community spirit in Blaengwynfi. When the coal industry flourished, it had a population of 10,000. It is now 2,000. When the local Co-op closed in 1983, 450 villagers set up their own co-operative venture, which now boasts a supermarket and six small businesses.
One of the founders, Malcolm Reeves, said: 'These people have a special spirit. They are determined to keep the community spirit. But for the patrols' prompt action when the shop was broken into last January, we would have lost thousands of pounds' worth of goods.'