Mark 25 warp sensor
The Mark 25 warp sensor was, in 2364, the most advanced warp sensor in the Federation. This unit had strategic importance. 

Two starships, the  and , were refitted with these sensors, and were sent to a particular sector for trial runs. Upon successfully completing these trials, both ships transmitted their findings covertly to the Advanced Technologies Division. 

The reason for this was that Starfleet was concerned that if the findings were transmitted on the normal subspace com network Ferengi agents might intercept these transmissions. (, okudagram)
Sensor technology