Sensor

It's labelled Short Skill which means active turn only, to use it in the Reactive turn it would need the label ARO or Short Skill/ARO.

You still benefit from the +6 to discover rolls in the Reactive turn though, and prevent enemies in your ZoC from re-camoing.

 

At the end of the core rulebook (pg246) there is a table with all the orders that can be declared, grouped by color and with a legend explaining each color. there, you will find Sensor as a Complete Order (when used for Triangulated Fire) or as a Short Skill (when used for discover purposes). That table also indicates the page of the rulebook where that order can be found.

In this case, since Sensor is not in the ARO column (3rd of the page, in yellow), it cannot be used during the Reactive turn. So no, you cannot.

That might not be the case. Since the 4th entry on the Sensor order would still require for you to declare Sensor, and be there for those pesky markers outside of the Zone of Control of the sensor troop.
The only way for that bonus to be applied during the reactive turn would be if it was on an Automatic Equipment piece of gear, instead on the box for an order.

 

Sensor does not have the ARO tag on its skill, you cannot use this skill as an ARO.

 

Sensor also grants its user, automatically and without making Rolls or spending Orders, a +6 MOD to WIP when declaring Discover against Camouflage or TO Camouflage Markers

Emphasis mine.

 

Yeah that part works just like any other bonus granted by a skill. You're not actually declaring Sensor as an ARO, but Having Sensor grants you a bonus when you declare regular old Discover.

 

Also if Sensor (as an equipment) was only to be used in active turn, you wouldn't be able to use the "Enemies with the CH: Camouflage or CH: TO Camouflage Special Skills cannot regain the Camouflaged or TO Camouflaged state inside the Zone of Control of a trooper with the Sensor Special Skill." rule.