Sensors, ECM, Active Probes, Hidden Units, and Initative.

Here is a brief run down on how sensors, hidden units, units out of line of sight and their effect on initiative will work in the game.

We will start with some definitions.  Active unit is any unit that is manned and capable of moving and/or shooting during the turn.  There will be times, when units out of line of sight, but will be capable of moving.  All active units are part of the initiative / movement phase.

The only way to know about the movement and location of the unseen active units is either with the sensors skill, or an Active Probe equipped mech. The Active Probe stacks with the skill giving the mechwarrior one sensor skill higher then he actually has. 

To represent this Non-LOS unit I will use a marker rather than the actual figure.  So in a city fight you may see 3 markers moving about 3 blocks away, but you won't know if they are light tanks or assault mechs unless your sensor skill is high enough and the sensor mechwarrior is in range.

When ever a unit moves into line of sight the marker will be replaced with the actual mini.

To make things a little more confusing, some units have Electronic Countermeasures or ECM.  These units will block all active probes or sensors (as well as a lot of other things like Artimus and C3 networks.)  A sensor unit will be able to tell they are being jammed, and will be treated like a regular unit without sensors.

There are times where units may start the game hidden.  Meaning the ambushing unit is running on minimal power and is camouflaged.  Hidden and non-active units do not count toward the number of units on a side for purposes of the iniative/ movement phase.  After a unit with Active probes or Sensor skill moves, it will detect these hidden units if they are within range.  This ambushing unit may not move or torso/turret twist without giving away their position.  So if they remain undetected, they may pop-up out of nowhere when they make their first move, twist or shot.   The only other way they may be detected is if a non-sensor / active probe unit finishes their move within 2" of the hidden unit.

There is the potential that some active unit may come into LOS and  then drop back out of LOS.  If this happens once they are out of LOS they will revert to the marker.
Finally, you may fire indirect LRM's at units but they must be in LOS to at least one of your units.  Meaning no firing at the markers, the unit has to be on the table to launch a volley at.