Long Range scans and surprise
Here is what I would do to work with Surprise and sensors:
Using my Sensors House Rule lets look at an example of two ships from the Starships book - a re-fit Constitution class and a B'rel:
Sensor Rating:
CONNIE - +3/+2/+1/0/0
Sensor Operator has a +11 (all ranks and mods)
B'rel +2/+1/0/0/0
Sensor Operator has a +11 (all ranks and mods)
Let's set up our encounter with the B'rel sneaking into Fed space (not cloaked) but Running Silent (EMCON 1) and the Connie running at SOP for Under Weigh (EMCON 2). Also let's assume that they are at a distance of 20 LY - the distance of Standard Resolution Long Range scans (the maximum scan range for sensors and 1 month's travel at Warp 5).
The Sys Ops (Sensor) test for the B'rel:
TN 10 + 0 (EMCON) + 6 (Range) + 0 (Sensor Mod)= TN 16
Roll - 9+11= 20 Complete Success
The Sys Ops (Sensor) test for the Connie:
TN 10 + 10 (EMCON) + 6 (Range) + 0 (Sensor Mod)= TN 26
Roll - 8+11= 19 FAILED
As Narrator I would describe the Klingon's results as such - 'Far off in distant space, the B'rel sensors detect radiation. Is it ambient radiation from a dying star or is it a Federation ship patrolling the sector? The Klingon commander decides it is too distant to concern with and keeps on their present course. He brings his ship to Warp.' (If it were the Connie, there is nothing to tell...)
Now lets bring our situation in closer, assuming the ships have been on a course towards one another. Both ships are at Warp Factor 5, 6 Light Years away and closing (9 days distant), and now are using their Long Range Sensors set to High Resolution at EMCON 2:
The Sys Ops (Sensor) test for the B'rel:
TN 10 + 0 (EMCON) + 6 (Range) + 0 (Sensor Mod)= TN 16
Roll - 10+11= 21 Complete Success
The Sys Ops (Sensor) test for the Connie:
TN 10 + 0 (EMCON) + 6 (Range) + 0 (Sensor Mod)= TN 16
Roll - 7+11= 18 Complete Success
As Narrator I would describe the two ship's results as such - 'Sensor scans have definitely detected a ship moving at warp, picking up the object and its subspace emissions. Is the ship a freind or foe? (for the klingon: is the ship a threat or prey?) Distance is still great between them and it is now worth the time to divert course and see who is out there.'
I may even allow a TN 25 or 30 Sys Ops (Sensors) or Compuer Use (Analyze) to determine the ship type from the emission. I may give affinity bonuses for some kinds engineering, knowledge, or science. Point is they know that something is out there, just not what. As they close, it would be worth it for the B'rel to go to EMCON 1 and then to cloak making them a hole in space and gain the definite surprise on the CONNIE.
Ships have now closed to 2 LY (1 day away) and they are still traveling at warp 5, Long Range Scans still at High Resolution (EMCON 2):
The Sys Ops (Sensor) test for the B'rel:
TN 10 + 0 (EMCON) + 0 (Range) - 1 (Sensor Mod)= TN 9
Roll - 5+11= 16 Superior Success
The Sys Ops (Sensor) test for the Connie:
TN 10 + 0 (EMCON) + 0 (Range) - 2 (Sensor Mod)= TN 8
Roll - 9+11= 20 Extraordiary Success
As Narrator I would describe the two ship's results as such - 'Sensor scans are tracking a ship moving at warp 5, its mass is (SIZE ??), and class may be determined by its warp signature.
I will require a TN 15 or 20 Sys Ops (Sensors) or Compuer Use (Analyze) to determine the ship type fromthe emission. I may give affinity bonuses for some kinds engineering, knowledge, or science as well as a bonus based on Degree of Success.
The ships close that last day and come within kilometers (Long Range 100,000 KM) of each other and switch from long-range scanners to short-range and lateral scanners. The Connie stays at EMCON 2, sweeping the area for any trace of the ship while the Klingon drops out of Warp and begins Silent Running (EMCON 1) as well as cloaks.
The Sys Ops (Sensor) test for the B'rel:
TN 10 + 0 (EMCON) + 4 (Range) - 0 (Sensor Mod)= TN 14
Roll - 7+11= 18 Complete Success
The Sys Ops (Sensor) test for the Connie:
TN 20 (CLOAKED) + 10 (EMCON) + 4 (Range) - 0 (Sensor Mod)= TN 34
Roll - 4+11= 15 Disastrous Failure
As Narrator I would describe the two ship's results as such - 'The Science Officer aboard the Connie looks up to his Captain and says that the ship has disappeared completely off of scanners.' (if they know the class from the above tests, they mayknow why.)
When the Klingon uncloaks, he will have complete surprise on the CONNIE and be able to take a Free attack (or whatever the Narrator awards the player). The only problem with making his ship 'disappear so completely' is that he will need time bringing systems back on line.
Anyway, this is how I would interpret my sensor rules into using LONG RANGE SCANNERS and trying to achieve some surprise. Without the cloaking device, the B'rel may not have gotten their surprise, who knows?