Despite recent scandals regarding privacy, Facebook is performing a study where they pay you to monitor your phone.
The study is through an app called Study. Through it, Facebook will monitor which apps are on your phone, how often you use them, what country you’re in, and more. Study will not gather information on websites, passwords, or any other specific content though.
Facebook actually tried this before, but it was shut down. They marketed Study to teens on iPhones. To participate, people had to use a special certificate that went around the App Store, which violated Apple's rules.
To be eligible, you must be 18 or older and have a PayPal account to be paid. You might also have to be targeted through a Study ad to gain access.
For more info, read The Verge's article.