Congratulations! You just won a $100 gift card!

That's what those emails and pop-up ads keep telling me, anyway.

Of course, I'd have to buy something (maybe several somethings) and jump through hoops (maybe several hoops) to get a "prize." And if I did that, then I'd get slammed by spam and/or telemarketing calls.

Scammers notwithstanding, it is possible to get gift cards for free -- sort of. Few things in life are truly free. You may have to click on an email, take a survey, utilize a specific search engine, attend a Twitter party, transfer a prescription, use a rewards credit card or maybe buy a few things you were going to buy anyway.

For the most part, you can get gift cards without spending a nickel. All it will cost you is time -- maybe a few minutes a day, maybe a little more.

Seriously: Would you really miss five minutes a day? Some people spend that much time staring into the closet and wondering what to wear. And if you're unemployed, on a tight budget or in debt, those few minutes could make a big difference.

Kymm S., an Iowa resident who asked that her full name not be used, spends about 15 minutes a day on MyPoints and Swagbucks. The two programs yielded her $200 worth of gift cards for the 2011 holidays -- a real boon in a lean year.

"I've been unemployed or partially employed for the past 17 months," she says, "and was very glad to have those (cards) available."

Even people whose books are currently balanced are aware that life can change without warning. That's why we're frugal. That's why we like free gift cards.

The old reliables

Start with established sites such as MyPoints, Swagbucks, QuickRewards and My Coke Rewards. But keep an eye out for new rewards programs. I just joined Superpoints, which is similar to the above-mentioned sites; it's invitation-only, but you can probably wangle an invite through its Facebook page.

A growing rewards trend is for e-coupon and location-based shopping apps like SavingStar and CheckPoints. Kenia Perales, a stay-at-home mom in Edinburg, Texas, earns points from seven such programs. They're easy once you get in the habit of using them, she says.

A bonus: "I let my children scan items at the grocery store for points, and that keeps them entertained."

Survey sites often give the option of gift cards versus cash. Do the math before committing, though. A company might require as many as 10,000 points for a $25 gift card -- pass! I once saw a site that let users trade points not for gift cards but for entries in gift-card sweepstakes. Riiiiight.

Tops among readers are PineCone Research, Toluna, Synovate, i-Say, Clear Voice Surveys and Valued Opinions.

How do you separate legitimate rewards websites from the scammers and spammers? Online user reviews are a good start. Or look for bloggers who recommend such sites. It's likely that they get fees for referrals, but a reputable blogger probably won't risk alienating readers forever to make one-time bucks.

'Splurge without guilt'

MyPoints is the granddaddy of the rewards programs, having been around for more than 15 years. Users can earn points in many ways, such as reading emails, buying things through the site (which has an affiliate relationship with many major retailers), playing online games and redeeming manufacturers' coupons.

Points can be cashed in for gift cards from dozens of merchants. Restaurant cards -- Applebee's, Panera Bread, Outback Steakhouse -- are quite popular, MyPoints President Matt Wisk says.

"It's an indicator of the economy at large," Wisk says. A restaurant gift card is a way "to splurge without guilt."

Or to buy Christmas gifts. Dallas resident Shellye Carpenter cashed in $275 worth of gift cards for Lands' End, Amazon.com and iTunes. The take was a little higher this year because she bought shoes and some bridesmaids' gifts through MyPoints. Generally, she spends no more than 30 minutes a day on the site -- and always while she's doing something else.

"If you're sitting there anyway, watching TV or 'Facebooking,' why not earn something for your time? I've always been a multitasker," Carpenter says.

Assuming you bought nothing and simply clicked through emails, an average of three a day would earn more than 5,000 points in a year. That will more than buy a $25 card and is almost enough for a $50 gift card.

This sounds slow, but sometimes frugality is like that: small steps leading to (eventual) rewards.

A personal favorite

Swagbucks is one of the most popular rewards programs out there, according to Becky Ford of CompareRewards.com. It's one of her personal favorites, in fact. Mine too: I paid for a chunk of my under-$100 Christmas with Amazon gift cards I got from Swagbucks. (For more, read "Christmas for less than $100.")

The site's search engine randomly awards "Swag Bucks" to users. (I've gotten as many 100 or more in a single day.) You can earn Swag Bucks in other ways, too, such as taking surveys, finding bonus codes and watching short videos. The company recently introduced an app that lets users watch movie trailers for credits.

Points can be traded in for rewards like gift cards, PayPal cash, electronics, music downloads, housewares, sports logo items and jewelry. Guess which is chosen most often?

"Gift cards are our most popular item. It's really one of the big draws to Swagbucks," Chief Operating Officer Scott Dudelson says.

As with other programs, the number of points you get depends on how much time you're willing to spend. On the Facebook page, users crow about earning hundreds of Swag Bucks per day. Recently, half a dozen users qualified for a survey that paid out 10,000 points. Yes, 10 grand.

All but one of the gift cards offered are e-gift certificates, good for Internet commerce only. If you don't shop online, you could give the cards as gifts or sell them on eBay or on the secondary market. Amazon and Target cards are particularly valuable. (For more details, read "How to sell unwanted gift cards.")

Party on -- online

Two other potential gift card sources: blogs and social media. A number of bloggers regularly offer giveaways to attract readers. Do an Internet search with keywords such as "blogger gift card giveaway," and you'll find quite the lineup. Often, entering is as simple as leaving a comment.

Another hot search term: "blogger Twitter party." This is an online social event whose hosts frequently offer gift cards to encourage attendance. Find the events through hashtag searches on Facebook or Twitter, or through sites like Twitter Party Guide and Resourceful Mommy.

You must register in advance to be eligible for a prize, and other requirements may exist (e.g., posting a comment confirming your participation). Don't just show up five minutes before the party ends and expect to snare a gift card.

But do show up. Perales has won as much as $500 worth of gift cards in a single month.

"I did all my Christmas shopping with gift cards I got from the Twitter parties," she says.

Save those bottle caps

I know that soft drinks aren't good for me, but what's life without a little sin? Especially if you can make your habit pay. The My Coke Rewards program offers points for codes found inside bottle caps (three points) and multi-packs (10 to 25 points). My favorite prize is the free movie ticket, but you can also get gift cards for restaurants and retailers.

Or lodgings. A reader named Nancy W. has used My Coke Rewards points for hotel gift cards when relatives hit town. She has cashed in for gift cards to Panera, Red Lobster, Bath & Body Works, Olive Garden and Omaha Steaks, too.

"I really can use (the income supplement), even though I have a full-time job," says the Pennsylvania resident, who asked that her last name not be used.

My Coke Rewards generally experiences "a big spike" in card redemptions every autumn, according to spokeswoman Susan Stribling. "We assume it's people giving Christmas gifts."

I'm there myself, having cashed in points for gifts like magazine subscriptions, a set of barbecue tools, a movie-themed T-shirt and a NASCAR hat.

The old switcheroo

Drugstores want your business, so watch their ads: Some offer gift cards if you'll transfer your prescription or fill a new one. Before I got into an HMO with its own pharmacy, I took pains to buy prescriptions from places that would pay me back. I also transferred prescriptions from place to place whenever possible.

Sometimes these programs are limited to first-time customers. But a pharmacy may define that as "someone who hasn't filled a prescription for six months." Read the fine print.

Note: If you take more than one medication, say so. Pharmacists need to be on the lookout for possible drug interactions.

If a coupon is required, clip it and put it in your wallet; that way, you're prepared for when someone in your family needs a prescription filled. Write the phone number of the most conveniently located pharmacy on the coupon, so you can get the doctor to phone it in.

The prize for the oddest drugstore promotion: a $5 CVS gift card for turning in expired or unused prescriptions, reported by a Florida reader.

Tips from the pros

The question is whether you have the time to answer surveys, click on emails or attend Twitter parties. Only you can answer that.

How much of your life you can devote depends on the kind of life you have. An at-home parent can answer surveys while watching the kids play in the yard. A light-rail commuter can click on emails via her smartphone.

Learn to work those gift-card giveaways with advice from those already who do:

• Spam happens. Start a separate email account. You'll also probably get newsletters, updates or bonus-offer emails.
• Branch out. Look beyond surveys and searches. "How MyPoints Works" explains all point-earning tasks. At the bottom of the Swagbucks home page is a "Ways to Earn" section; an independent online guide called Swagging 101 is a big help, too.
• Hint, hint. Check the Swagbucks Facebook page from time to time, and watch for "thanks for the code!" messages from members. When you see one, start looking for a "Swag Code."
• Workplace points. In charge of ordering office supplies for the office? See if what you need is available through a rewards site.
• Down and dirty. If you're not squeamish, check the lunchroom recycle bin for Coke products. I look for caps everywhere, and I find them. Lots of them.
• Be patient. Points do add up. In time you will have enough to buy something for someone else or for yourself -- especially if you get chosen for a 10,000-point survey. I wish.

Donna Freedman is a freelance writer in Seattle. You can find more of her writing on MSN Money's Frugal Cool blog and at Surviving and Thriving (motto: "Life is short. But it's also wide.").