If you have a lot of free time, you can use your smartphone to earn satoshis which is the basic unit of bitcoin. Just try some of the legit bitcoin faucet like
1. Bitfun http://bitfun.co/?ref=B41A7C9A4B43
2. Moonbit http://moonbit.co.in/?ref=70c225c75c4e
You'll earn just small amount of bitcoin ...