Recs.
Updated
Perk is an application you can use to stream ads to your phone. It is most effective when running constantly, which means it is best used on an old phone (or a budget phone purchased specifically for Perk).
Specs
Pros
Pro Use up to 5 devices at a time to maximize profits
This is known as a "Perk farm" - when you have multiple devices (up to 5 are allowed on a single account) all running Perk at the same time. Using 5 devices constantly streaming ads can yield somewhere around $50/month in the US (not as much in other countries).
Cons
Con It's a bad thing to do
As annoying as ads can be, these are people paying, hoping to bias your mind. If you don't hear or see the ads, you're basically exploiting the people paying for it. Also remember to deduce your electricity usage.
Con Phones have to continuously stream ads
Phones with Amoled displays are prone to burn in when used excessively, so their screens may be ruined if you stream ads on your phone all day.
Streaming ads will also put strain on your internet, and if you have a datacap it could fill up that cap.