Hidden hold on your cash.(debit cards)

On her way home from shopping one day last June, Kelly Maguire stopped at an Arlington, Va., Hess station and bought $19.10 worth of gasoline using a debit card.

The next day, when Steven Maguire, her husband, checked their account online, he discovered that Hess had frozen $50 of the checking account.

"We assumed that because we used a debit card, the amount was immediately withdrawn from our account," Steven Maguire says.

In fact, payment for the gas was transferred to Hess within 48 hours. The $50 block stayed active for another day, however.

The Maguires' experience wasn't unusual. They lost the use of their money for three days because of the kind of debit card they have and the way in which they used it. The card bears a credit-card logo, as many debit cards do. When Kelly Maguire bought the gas, she didn't enter a personal identification number, or PIN.

Many debit-card transactions--checking into a hotel, buying groceries, renting a car, or paying for a restaurant meal--don't require the use of a PIN. In those instances, merchants may block a portion of your checking account to ensure they receive payment. The hold is often 150 percent or more of what you actually spent. ...