The popularity of mobile payment methods make smartphones an easier, more secure substitute for paying for goods and services, but many people may not know that their smartphones can also be useful for earning money.

Alas, these apps will not make anyone filthy rich, but if they can help you pay for your next latte or even get a free lunch every now and then, then they are worth checking out.

A word of caution, however. Always read the fine print when downloading apps that claim to help you make money. While, for the most part, apps downloaded from the Apple App Store and Google's Play Store are fairly safe because of Apple and Google's security measures, some of these apps will give you money in exchange for information you didn't know you were sharing.

For instance, an app can access your phone's GPS to find your location, download files without telling you, take pictures and record video and audio, send messages without your permission, or even modify or delete the contents of your phone.

"Yes, they need to monetize you and ensure that you're located where you say that you are, but they're collecting way too much information," says cybersecurity expert Gary Miliefsky.

However, if you're keen on making an extra buck or two from an app, always make sure that you read the app's privacy policy, check out what type of information it collects, and download only from reliable sources, that is, the App Store and Play Store. Never, ever download an app that appears as a text link in an SMS.

Here are legitimate, money-making apps worth checking out:

i-Say Mobile (iOS, Android)

i-Say Mobile is an app developed by Ipsos, the survey company that is very popular because they are always seen taking surveys during presidential elections. i-Say invites its members to take surveys, the highest-paying and also rarest of which cost as much as $95. Most other surveys, however, earn you a few dollars and points that can be redeemed as Amazon, PayPal, and iTunes gift cards. You need to sign up at the i-Say website to become a member.

Swagbucks (iOS, Android)

There are nine ways to make money on Swagbucks. You can browse the web, take surveys, shop in the Swagbucks mall, vote on daily polls, play games, watch videos, find swap codes, complete special offers, and bring in your friends to sign up. Swagbucks earnings come in the form of virtual money that can be redeemed as gift cards, coupons, and sweepstakes entries.

SlideJoy (Android)

You might as well get paid for the amount of time you check out your phone. SlideJoy puts product ads on your phone's lockscreen and pays you a fixed amount every time you unlock your phone, whether you look at the ad or not. Users say they earn $5 to $15 on average with SlideJoy.

App Trailers (iOS, Android)

App junkies, this app is for you. App Trailer shows its users 30-second video trailers of new apps to download and install. For every app trailer you watch, you earn money. For every app you download and engage with, you earn even more. The more trailers you watch, the more points you earn, which can then be converted into gift cards or redeemed via PayPal.

InboxDollars (iOS, Android)

More than $30 million have been paid out to InboxDollars users since the long time it has been around. You get $5 alone just upon signing up. InboxDollars' main attraction is it pays you money to surf web, play games, and take surveys. Users can cash out by requesting payment via check once they earn $30, which is completely possible in a couple of hours.

Viggle (iOS, Android)

Viggle wants to know what songs you listen to and what TV shows you watch, in exchange of course, for points that can be redeemed as gifts cards, digital downloads, electronic goods, and trips. Simply open the Viggle app when you watch TV or listen to music and you start collecting points.

Mobee (iOS, Android)

Be a mystery shopper for Mobee's partner stores and earn points that can be exchanged for cash, gift cards, or even event tickets based on the quality of your evaluations. You can download the app for free to check out what missions are available in your area. Each mission earns you anywhere between 150 points ($1.5) and 3,000 points ($30).

Receipt Hog (iOS, Android)

Receipt Hog lets you take pictures of your receipts in exchange for coins. Each 1,000 coins can be redeemed as Amazon gift cards or as cash via PayPal. As you upload more receipts, you unlock more ways to earn money, such as taking surveys.

Perk (iOS, Android)

The Perk app offers a variety of ways to make money. For everything you do in one of the Perk services, such as when you search, browse the web, or watch TV, you earn a small number of points. If you buy something off Perk Shopping, you earn a massive amount of points that can be converted into gift cards. Minimum payout for Perk is $5.

Field Agent (iOS, Android)

Instead of having you browse the Internet or take surveys, Field Agent pays you to do small tasks for its clients. For instance, you can earn $9 taking four different photos of toothbrushes at Wal-Mart or $5 checking out the price of certain dolls at Toys "R" Us. Taking into account the time and gas it takes to drive out and accomplish those tasks, you'll still be able to make up to $20 as a field agent.

TaskRabbit (iOS, Android)

The great thing about TaskRabbit is that it pays you more than double the minimum wage to complete simple tasks for people in the community, such as putting together IKEA furniture or walking the dogs. However, you'll have to apply to become a Tasker, background checks and all.

ESPN Streak for Cash (iOS, Android)

Want an app that can pay you $50,000 a month? ESPN Streak for Cash pays you if you can have the longest streak of correct predictions on upcoming games. Only one person gets the 50 grand, though, so you better make sure you know your sports very well.

Bookscouter (iOS, Android)

If you have a lot of books gathering dust on your shelves, Bookscouter can help you look for buyers offering the highest amounts. Simply scan the barcode of your book and the app will give you a list of buyback companies and their prices. Once you choose your seller, give them your payment details and ship the book to them.

Pact (iOS, Android)

There is nothing like getting paid to lose weight. That is the premise behind Pact, which pays users $5 every week for accomplishing certain tasks, such as eating a certain number of healthy meals or exercising a certain number of hours for the week. Is it effective? Pact says 92 percent of its users are motivated to lose weight, not just because of the $5 weekly reward but also because of the $5 penalty if they fail to complete their tasks for the week.

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