Shops and off-licences in a part of Carmarthenshire are no longer selling alcohol to anyone under the age of 21 at weekends.
The move introduced in villages in the upper Gwendraeth Valley is aimed at combating anti-social behaviour.
All outlets selling alcohol in the area have signed up to the voluntary scheme.
Dyfed-Powys Police said many under-age drinkers in the area were getting their alcohol from friends in the 18 to 21 age bracket.
Most supermarkets warn customers they will be asked for identification if they look under 21.
But police community support officer Ciaran Ryan said the initiative went a step further, stopping under 21s buying alcohol on Fridays, Saturdays and Sundays.
It's been running two weeks and we have not had a single call since then
Ciaran Ryan, PCSO
Mr Ryan said: "We've had local residents complaining about under-age drinking.
"There are an older number of youths - 19 or 20 - who hang around with the younger crowds who are buying it.
"Every licensed premises in the area has joined and it runs side by side with other schemes such as Behave or Be Banned and Pub Watch.
"They were all very much for the idea - a lot of them were keen to be shown to be cooperating.
"It's voluntary but the licensee has the ability to refuse alcohol to whoever they want.
"It's been running two weeks and we have not had a single call since then."
All 12 outlets in the area which includes Cross Hands, Gorslas, Tumble, Llannon and Drefach have joined.
Gail Anderson of Cross Hands Stores said the stores had backed the scheme.
She said: "I think it's a good idea - the older ones who were 18 were buying for the younger ones which was the problem.
I think it's a bit crazy because you are an adult at 18, you've got a vote at 18 and you can get married at 16
Janet Jones
"They would go to the park or the underpass down the road."
A survey published earlier this year by The World Health Organisation survey of Europe and North America found more young people in Wales had been drunk at least twice by the age of 13 than anywhere else in the western world.
A quick snapshot of opinion on the scheme found many in favour.
But Janet Jones said: "They are on about binge drinking but it's been around for years and years and it's nothing new.
"I think it's a bit crazy because you are an adult at 18, you've got a vote at 18 and you can get married at 16."
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