ORLANDO, Fla. -

Point, click, deposit -- it's so simple that 20 million people are using mobile banking apps and by the end of the year, that figure is expected to grow to 30 million.

[WEB EXTRA: Double deposit warning]

But as with all new technology there can be troubles.

For Geri Detweiler, it all started with a phone call telling her a check she wrote to a charity was cashed twice.

"My first reaction was, 'How did this happen?' My second reaction was, 'Oh no, have I bounced any checks,'" said Detweiler.

The check was first deposited by the charity virtually by simply pointing, shooting and clicking using a smartphone deposit app.

The second time, an employee went to the bank and mistakenly deposited the same check number 1027 again.

The bank didn't catch the duplicate deposit and Detweiler's account was hit twice.

"I think most people would be shocked to learn that a check that they write could be deposited twice," she said.

"Generally if there is a duplicate deposit the check writer's bank will catch it, and the check writer never knows anything about it," explains an expert with the American Bankers Association.

But if your bank doesn't catch a "double debit," the ABA said the bank should refund your money and any fees associated with the bounced check.

With digital banking becoming so popular it's important to be proactive. You should always have your bank alert you if your balance goes below a certain amount.

Also ask what system they have to detect duplicate deposits, and your best option is to log on every day to check for errors.

What if you're on the flip side and you mistakenly double deposit a check? The bank should reverse the charge and there should be no trouble if it's an honest error.

But banking expert Betsy Didan said banks are watching everyone's digital deposit habits more closely nowadays.

"If they have any abuse to the system, they will actually shut down the application if they feel the consumer does not handle it appropriately," said Didan.

In Detweiler's case, she didn't bounce any checks and the charity reimbursed her for the double deposit.

"I've learned a lesson here," she said.

One more tip: after you make a mobile deposit, keep the actual paper check for a week or two, and mark it with a small check or tear the corner so you can tell you've already deposited it.