Social network Foursquare has started rolling out full-page post check-in ads in its mobile apps. The ads are presented to users immediately after they check in at certain locations, typically offering a relevant suggestion or coupon. The Diageo-owned Captain Morgan rum brand is one of the first on board. For example, users who check in at certain bars or restaurants will be served an ad suggesting they order a “Captain and cola” or “Captain mojito.”

“Diageo plans on advertising its vodka brand Smirnoff via Foursquare post check-in ads starting in August. The Captain Morgan campaign began on July 1 and is slated to run for four to six weeks,” reports Advertising Age. “The new post check-in ads join promoted listings within the ‘explore’ tab. Pricing for post-check-in ads is on a ‘per action’ basis, meaning brands are only charged when a users taps on the ad or saves it for later use.”

“The new ads are also being used to help retailers or merchants lure consumers who check in outside of their locations. Toys R Us has started to use this capability by targeting people who check in at family-friendly locations such as parks, playgrounds and daycares. A June 19 post from website About Foursquare shows the author being served a 20 percent off, limited time use coupon for use a Toys R Us or Babies R Us after checking in at a public swimming pool.”

Foursquare recently reported more than seven million unique visitors via smartphones for certain months. Engagement has been consistent over the past year, with users typically opening the app 10 times per month.

“Foursquare has been very careful about how it monetizes,” notes The Verge. “The company has amassed a sizable user base of 35 million, but skeptics have long questioned how Foursquare could effectively monetize its service. Last year the company introduced promoted updates, which operated much like Google AdWords. The sponsored posts would show up when users searched for a place to go, and advertisers would pay Foursquare if users clicked through.”

“Foursquare also works with businesses to offer coupons and other promotions. All of the different types of ads, including the ones introduced today, focus on relevancy. To-date that has helped the company make sure ads don’t scare away users, but as the Foursquare dives in to full-page units we’ll have to see if it can pull off the same feat,” suggests The Verge.

“While the whole thing sounds like it will get really annoying really quickly (‘You just checked into Arby’s — why not buy some antacid?’), these new ads could be supremely relevant,” comments VentureBeat. “If Foursquare knows you’re in a bar (because, er, you told it so), it’s in a really good position to pitch you things you might be interested in. And this approach makes a lot more sense than sending all Foursquare users the same Taco Bell promotion.”