Banks used to deny debit card purchases or withdrawals that would overdraw your checking account.

Now they're happy to approve those transactions under the friendly-sounding phrase of "overdraft protection" -- and charge a fee for insufficient funds.

Banks will also bounce any checks that show up for payment, imposing additional penalties for each of them, until you deposit enough money to get back in the black.

A study by the Center for Responsible Lending found consumers typically overdraft less with a debit card than a check -- $14.75 vs. $31 -- but incur a higher fee -- $34 for the debit card purchase vs. $31 for the check.

Click here for more of Interest.com's smart owner's guide to debit cards .