The tallest office building in Denver contains one of the city’s tiniest convenience stores.

The little shop, which has no employees, is managed by Ray Huff’s HJB Convenience, which specializes in c-stores in office buildings.

Office workers punch in their work phone number to open the door for five seconds. They check themselves out after they make their purchases with a custom point-of-sale built by Tenderfoot Software, which Huff also founded. This is the second iteration of the unmanned Russell’s Express c-store, and sales are even better here than in the first unit, which has been in operation for about three years.

For both of the unmanned stores, nearby units with human employees act as fulfilment centers. Huff and his teams at HJB and Tenderfoot built the unmanned stores from the ground up.

He credits his team of younger programmers for helping to make Russell’s Express a reality. “Older people, the ‘seasoned’ ones, have a box around them, where the younger people don’t have that box,” says Huff. “Look at the new store we just opened. All of the millennials and the young people, they got it right away. The old people were even afraid to type in their phone number.”

As more stores introduce checkout processes that circumvent the need to wait in line, Huff is determined to stay ahead of the trend.

“If you’re talking five years from now, I think every one of my stores is going to be almost fully automated,” he says. “People have phones. Heck, they’ll go without their wallets before they go without their phones.”

“All of the millennials and the young people, they got it right away.”