Like many Americans, Paquin thinks about the importance of saving more often than she actually saves. In a 2015 Federal Reserve Board survey, 46 percent of respondents reported that they would have trouble coming up with $400 in an emergency; living paycheck to paycheck is now a commonplace middle-class experience. So while Paquin noticed that her Walmart MoneyCard app asked her from time to time whether she wanted to “stash” some money, she didn’t bother to figure out what that actually meant, let alone respond.

Then, late last year, she got an email saying that a “prize savings” feature had been added to her card. If she kept some of her balance in a virtual “vault,” meaning that it would not show up in her available funds, she would be eligible to win a cash prize in a monthly drawing—up to $1,000. Every dollar in the MoneyCard Vault would equal an entry in that month’s drawing. This caught her interest. A prize would go a long way toward her being able to buy a car. It also made her focus on what all those “stash” requests were about. “Oh, cool, this can work as a savings account, too,” she remembers realizing. So when she got paid, she started setting aside “10 bucks, 20 bucks, whatever I could.”