Sentinels do not always have to fight.
Receive $REN after staking Sentinels for a certain amount of days.

Passive Mode Rewards (Polygon)

Daily REN Rewards

(OLD) Rewards based on days staked Ethereum:

(discontinued after May 9th, you will not be able to send any new transactions in Passive Mode on Ethereum. However, you may return at any time.
0-6 days
0 $REN
7-13 days
140 $REN
14-29 days
420 $REN
30 days
1200 $REN
Note: You do not accumulate $REN daily, but receive the reward after you Unstake