ScreenLift Rewards is a screenlock app. It has a 4.3 rating on Google Play and there are over 50k downloads.
It is very easy to earn on ScreenLift. Simply enable the lockscreen feature and you will get credits (called Lifts) for unlocking your phone. Your Lifts count is updated once every hour.
They pay through Paypal and giftcards (Amazon, Google Play, and Walmart). To cashout for $1 in your currency, you need 1500 Lifts. Payments are made only in your country's currency. They pay within 3 business days.
They don't specify which countries are allowed to use their app, but I don't live in a tier 1 country and I can use the app fine. If the app is available in your Play Store, it's probably available in your country.