Peering through the rain-streaked windshield of an unmarked car, Boston Police Detective Eric McPherson watched as a 17-year-old girl made her way across Washington Street and into a local liquor store.

“If they’re doing their job right, this ought to take 20 seconds,” McPherson said.

Now in his third week as a C-11 detective, the Four Corners native spent Thursday night providing backup for a series of alcohol compliance checks meant to ensure that area package stores follow procedure and card customers they suspect are under 21 as part of the precinct’s continued efforts to crack down on underage drinking.

The girl, a Chelsea resident brought into the neighborhood through a partnership between the Dorchester Substance Abuse Coalition (DSAC,) BPD, and her local substance abuse organization, left the store empty-handed, entered another detective’s car and headed off to attempt another buy.

“She’s not going to have any luck tonight, and that’s a good thing,” McPherson said. “She looks young and it’s a tough economy, nobody wants to get their business in trouble at a time like this. They’re taking heed of the warning.”

Within two hours, the team visited eight liquor stores ranging from small bodegas on Dorchester Avenue to the high-traffic outlets running along Morrissey Boulevard before returning to the precinct, happy to report that their underage buyer had been carded at every stop.

Among those pleased with the night’s outcome was C-11’s Captain Richard Sexton, the district commander, who said the operation was part of an ongoing effort to curb underage drinking. The problem typically spikes during the summer months and around the holidays, Sexton said.

While detectives targeted liquor stores with “some randomness,” Sexton said, several of the shops had been cited in past stings, while others had come to the precinct’s attention following complaints from residents.

Stores caught selling alcohol to minors during these operations are not immediately fined, but are instead called before the Boston Licensing Board where they could face a temporary suspension of their liquor license, extensive fines, or lose their license completely and be forced to reapply before alcohol can return to their shelves.

In previous years, underage police cadets were used during compliance checks. However, a shortage of officers in training has recently prompted C-11 detectives to partner with members of the Dorchester Substance Abuse Coalition, which brings in teens from sister organizations across the state as a way to ensure those involved do not run afoul of local shopkeepers.

When asked about her experience as a designated buyer, the teen, who has asked to remain anonymous, said that she has been on a number of compliance checks in other towns and felt the evening was well-spent. She feels she is doing her part to keep kids above the influence.

“In school they talk about what we can do to help other kids stay away from drugs and alcohol,” she said. “I don’t drink and I don’t smoke, so I think ‘why not help the youth of the community stay clean too?’”

DSAC prevention services supervisor Meg Rose was also involved in Thursday’s compliance checks and said that their partnership and information-sharing with police is just part of her organization’s efforts to keep alcohol out of the hands of minors.

In recent months, DSAC began what they call a “shoulder tap” campaign, in which youths ask adults entering liquor stores to make a purchase, only to inform them of the potential fines they would face had the request been legitimate. Rose said that while some of her group’s outreach methods might seem unconventional, they have proven to be vital tools in keeping alcohol out of the reach of youngsters.

   “There are so many different ways in any community that a youth can get access to alcohol,” Rose said. “If they want it, they can be pretty resourceful. What we’re trying to do is reach out in new ways and make sure kids, parents, and businesses know the facts about underage drinking.”

To that end, DSAC most recently launched an awareness campaign on Oct. 28, in which 26 local businesses, ranging from health centers to bars and liquor stores asked employees to wear T shirts reminding patrons that purchasing alcohol for minors can carry fines up to $2,000 or prison time.

While Rose said there was much work to be done, she commended everyone involved in the compliance checks for doing their part – liquor stores included.

“I think that [the outcome] was amazing,” Rose said. “I was so excited when she came out without any alcohol every time. The fact that people were very much following the rules is a great sign for the community and the businesses of Dorchester.”