Long Range Active Sensors
This high powered sensor array can scan 4,200 cubic light years of space (in a sphere out to a maximum range of 10 light years). Only large objects will be detected at this range, unless they are emitting energy/radio waves or are travelling at warp speed. Therefore planets would be detected, along with any radio waves from those planets, but the small ships travelling at sub light speeds between the planets would not be detected.
Power Requirements
The long range active sensors each draw 50MW when they are in operation, regardless of the damage to them.
Upgrades
Research can be used to increase the scanner range and reduce the power required.