Just as many clouds have silver linings, many silver linings have clouds. For example, take a look at a few of the new developments in the credit card world:

  • More and more often, when you make modest purchases at many retail establishments -- purchases totaling less than, say, $25 -- you no longer have to sign anything. Retailers now offering signature-free transactions include McDonald's, 7-Eleven, CVS (NYSE:CVS), and Walgreen (NYSE:WAG). [Some, like Yum! Brands (NYSE:YUM) division Pizza Hut, are resisting, arguing that signatures prevent fraud.]
  • Some newfangled cards with embedded chips in them permit you to make purchases by merely waving your card over a reader, instead of the current swipe-and-sign process.

The cloud
Those may seem innocuous enough -- and even welcome. But here's a downside: This can all cost us more.

Let's back up for a second. We each make a decision whenever we pay for something: Cash or charge? It seems that when we charge, we tend to spend more -- presumably because it seems less like we're spending our hard-earned money and more like we're paying with imaginary money.

Check out this info from supermarketguru.com:

In one study, researchers asked several hundred families to do all of their buying with cash over a three-month period. At the end of three months, the same families were asked not to change their spending habits, but to use a credit card instead of cash to make their purchases. When they used plastic, the amount they spent rose between 20% and 30%.

In another study, a researcher at Purdue University instructed two groups of people to buy a pocket camera. He asked one group to pay cash for it and the other to buy it with a credit card. The group that used cash paid an average of $29.58. The credit card group paid an average of $52.67.

That's bad enough, but it gets worse. When we don't have to bother signing, it seems we tend to spend more. As Joyce Smith reported in the Kansas City Star, "While MasterCard (NYSE:MA) would not release figures, Visa said in 2005 its credit and debit cardholders spent $49 billion on small-ticket purchases, up 25% from 2004."

According to AMonline.com, during a MasterCard test program of "contactless" payments in its PayPass program, the company "discovered a 28% increase in weekly transaction volume among its PayPass account holders compared to the previous year when the technology was nonexistent." Want more? "American Express (NYSE:AXP) claims that contactless payments can be authorized and executed up to 53% faster on average than comparable credit card transactions and 63% faster than when cash is tendered. Additionally, merchants reported a 12% increase, month over month, in transaction volume after implementing a contactless payment option."

Those kinds of findings suggest that we'll soon see a heck of a lot of super-convenient, contactless purchasing opportunities. The PayPass technology is already being installed in Nokia (NYSE:NOK) cell phones, for example.

What to do
Fortunately, you're no longer one of the uninformed masses, charging more unwittingly. You're now among the savvy, clued-in elite. That means you can be vigilant when you use your credit cards in the future, paying attention to what you charge and trying not to overdo it just because it's become so darn easy.

Learn much more about the surprisingly interesting credit card industry in our Credit Center, which also features tips on getting out of debt, along with guidance on how to manage your credit effectively. Really. I mean it. There's some great stuff in our Credit Center, and it's all free reading.

The following articles can also help you:

MasterCard is an Inside Value recommendation and CVS is a former Stock Advisor pick.

Longtime Fool contributor Selena Maranjian owns shares of McDonald's and Yum! Brands. The Motley Fool is Fools writing for Fools.