I have that set up on my credit cards to alert me for ANY amount and here's why. I got an early morning phone call from my Capital One credit card about a 57 cent purchase on the card, which they took to be a "testing" charge ... nothing big that would raise alarms but so small I might not notice. They said that's a trick of fraudsters to see if the card holder is paying attention, and if they're not, they'll go back and charge something big.
Cap One was on it immediately. The card was cancelled and they issued me a new one.
Be vigilant!