Drift-Rite Indicators do both. The key is a 90-degree connection that links the leader to the Leader-Wise Pin so that the pin becomes a direct extension of your leader. The pin always points at your flies and any disruption of the flies, hitting the bottom or a take, is immediately telegraphed to you through movement in the pin.
When the pin is straight up and down your flies are directly below the indicator and the drift is most effective. If the pin is not straight up and down mend toward the flies.
When a fish eats your flies the pin will yell at you to SET.