Think carefully before handing over a debit card at a hotel front desk.

After saving for a San Francisco vacation, Manhattanite Lauren Hopkins checked into the Oakland Marriott City Center in August and was asked for a card to cover incidentals she might incur, such as meals, Internet connection or minibar snacks.

Hopkins, 23 — who, to avoid overspending, doesn't use a credit card — thought she had more than $600 in her account until her debit card was refused at a restaurant that night. It was over the limit, she says, because the hotel mistakenly billed her again for two nights' lodging, plus held $300 for possible incidentals without her knowledge. Because her card is tied to her checking account, she was broke.

Though hotels routinely put a hold on a card for the room rate and tax when a reservation is made to protect themselves from those without money to pay and to avoid losing revenue for no-shows, "there is no standard industry practice" for guaranteeing incidental payments, says lawyer Banks Brown, general counsel for the American Hotel & Lodging Association.

Some hotels place no holds on guests' cards for incidentals; others might hold $50 a day or more. "The practice makes sense because (hotels) know from statistical data how much people tend to spend on incidentals, and (hotels) want to ensure they are paid," Brown says.

Consider the experience of Scott Huelskamp, editor of a trade publication for rehabilitation professionals. When he checked into The Red Rock Casino Resort Spa outside Las Vegas for a conference, he gave the hotel a debit card — and later discovered that the hotel was holding $150 for each of the two nights he was there.

Back home in Wayne, Pa., his wife tried to use their account, leading to overdraft fees. Although the $300 was credited back, it took a few days.

Brown says problems were created when debit cards became more popular.

Consumers need to understand that a hold on a credit or debit card when you arrive "is for much more than you think your bill will be when you check out," says Ed Mierzwinski, consumer program director for the U.S. Public Interest Research Group. "Most people aren't totally maxed out on their credit cards, so they don't notice a hold. But people are closer to zero in their banking account" and don't realize they can lose access to money they haven't really spent.

Releasing holds can take some time, Brown says. First, a hotel accounting department must release a hold; then a bank in the card-processing chain must remove it. "Hotels are unable to release (funds) themselves" and can't control the timing, he says.

Some lodgings won't take debit cards because of potential problems.

"We have a sign on our counter that tells what's required, and we do not recommend using a debit card," says Jeanne Hizon, sales manager for the Executive Hotel Vintage Court in San Francisco.

According to Erica Harvill, a spokeswoman for MasterCard Worldwide, which offers both credit and debit cards: "We don't put any rules or regulations on how long a hold will be in a place. We recommend that cardholders check with the bank that issued the card" when dealing with hotel holds.

As for Hopkins, who works in administration for a New York law firm, she spent hours wrangling with the hotel.

"The person at the front desk gave me $100 in cash but said she couldn't get the money put back in my account because it was a weekend," Hopkins says. It took about a week to get her money back.

In the end, the hotel refunded the amount of her stay. But "it was so annoying," she says. "I had spent so much on this trip — and I really didn't enjoy it."