Of course, it's not a simple matter of buying gas or giving to charity -- if those tasks triggered alerts constantly, no one would do either with a credit card. But Levin points to another possible explanation: Purchases made in a high-crime area are going to be held to a higher standard by the bank.
"It's almost a form of redlining," he says. "If there are certain [neighborhoods] where they've experienced an enormous amount of fraud, then anytime they see a transaction in the neighborhood, it sends an alert."
(Indeed, Erin tells me that one of the gas purchases that triggered an alert took place in a rough part of Detroit, which she visited specifically for the cheap gas.)