"Life hacks" is one of those trendy phrases that describes strategies people use to be more efficient. But you know that.You probably also are well aware that you'll often see online articles with headlines like, "Life Hacks to Save You Money." Many life hack ideas are smart, but often the breezy advice attached to the life hack forgets to mention there may be a hidden cost, too. If you hear any of these life hacks mentioned, don't discount them, but do your homework to make sure they're actually saving you money.Life hack: Use coupons at stores to save money, and you're really missing out if you don't look for coupon codes when you're ordering food online.Why this life hack can cost more than you would think: Couponing only works if you were going to buy the item, anyway. You're probably also better off if you don't let couponing become a way of life."Years ago, I attempted couponing, when it was all the rage," says Kristie Garduno, a business owner in Newport Beach, California. "I took the time to learn all the tricks and lingo and even joined a group, so we could swap coupons. I started spending more and more time trying to save money, even skipping church so I could be first in line to get a good deal on an item – that I probably wouldn't use."[See: 12 Shopping Tricks to Keep You Under Budget.]Garduno says she went way overboard, scouring the internet, looking for deals, sometimes ignoring her business, a retail website called GivingSoaps.com. She even remembers getting in arguments with cashiers over 25-cent coupons."It became almost an addiction, and I'm grateful that I stepped away when I did," Garduno says. "I have no idea how much money I wasted in the name of saving." Life hack: Do a credit card balance transfer to save you money on interest. You apply for a credit card with a low introductory annual percentage rate (APR), preferably zero and one that will remain low for 12 to 18 months.Why this life hack can cost more than you would think: Yes, transferring money from a credit card with a high interest rate to a lower interest rate can be a good idea. But some credit cards have a high annual fee, negating the savings you're going to get. Other cards have a balance transfer fee, and while it may only be 3 percent, that adds up if you're, say, transferring $5,000 from one card to another. In fact, it adds up to $150.And you'll really blow it if you miss a payment, which happened to J.R. Duren, a copywriter in Jacksonville, Florida.In 2009, Duren transferred about $3,300 from one credit card to another. All was well until he was late with a payment and saw his interest rate jump 7 percent. It wasn't a financial disaster since he paid off the card by the end of the year, but he undid some of the work he was trying to do in saving money."I'm guessing the mistake cost me at least $130," Duren says.And keep in mind it's a terrible life hack if you transfer money from the high interest credit card to the lower interest rate one, and then later you end up maxing both of them out and carrying revolving debt.[See: 12 Ways to Be a More Mindful Spender.]Life hack: Buy in bulk. You know how it works. Buy a pack of 16 paper towel rolls at a warehouse discount store, and in the long run, it's cheaper than buying a pack of four paper towel rolls at a supermarket. You spend more upfront, but over time you save money.Why this life hack can cost more than you would think: Buying in bulk can backfire, especially if purchasing perishable items. Tyler Riddell, who works in marketing and lives in Temecula, California, says, "Every time I go to Costco, I think I'm saving tons of money by buying in bulk when in reality, only half of the items I buy get eaten while the rest goes bad and ends up being thrown out."Life hack: If you're looking for a new bank, sign up with one that offers a cash bonus.Why this life hack can cost more than you would think: You really want to be careful when you choose any monthly service, whether it's a bank or a telephone plan, that offers you money to sign up. The deal being offered may be good, but the company is going to get their money back somehow. Tyler McIntyre, a New York City-based business owner in the banking industry, says he once signed up for a bank's checking account offering a $200 sign-up bonus. Before long, however, he realized he was being charged a $12 monthly fee for owning the account. In less than two years, McIntyre's signing bonus would go right back to the bank, and he would still be paying $12 a month.[See: 12 Millennial-Inspired Ways to Spend Less.]That didn't sit well with McIntyre, who knew he could get the same services for free from a community bank."I closed the account, and they took back the $200," McIntyre says.11 Expenses Destroying Your Budget.