It's part of Legends now, but in the novel Shadows of the Empire, where Luke, Leia, and Vader are all on Coruscant (though not all in the same location), there's a point where Luke reaches out to Leia with the Force, and she responds. Vader picks up on this, is roughly able to determine that it's Luke he's sensing... but there's also a weird sort of "echo" effect as though there were two Force users instead of just the one, since he had no idea who Luke was reaching out to. Vader ultimately writes it off as he was far more focused on "dealing" with the story's main villain Xizor (who'd been a pain in Vader's armor-plated hindquarters throughout the story).

Something similar could have happened at Bespin, where Vader was so focused on just Luke that he ignored anything Leia might have been doing as an untrained Force-sensitive as what amounts to background noise.

Also worth noting re: Kenobi, Vader, and the Death Star: the entire "rescue" was staged as a trap, the heroes were allowed to recover Leia and escape with minimal challenge and pursuit. Even if Vader knew precisely what Kenobi was up to the entire time (and he probably did), it served the Empire's purpose to let them succeed. Vader intervened when their escape was almost complete in order to deal with the wild card Kenobi, and take revenge on his former master.

My take on detecting Force sensitives is that it is difficult to do if the subject is not actively using the Force, unless that person has a pre-existing strong personal connection to the one doing the searching. Then you might feel a ripple if that person is close enough, particularly if they are experiencing strong emotions, or are in danger, or committed to a task.

One thing...Active force use ripples the pond as it were. The bigger the use the bigger the ripple.

This is how it is portrayed in the movies guys, why does Luke sense his friends Foresee. How does Vader sense Luke originally you might ask, Luke most likely was using a massive amount of Force Powers on that Trench Run that is the only way that shot could be made, additionally you can't sense someone who is not yet begun the training, Luke's training began with Obi-Wan on the Falcon. Also why would the character lose the squad if he became an Inquisitior if I was GMing I would say he becomes an Inquisitor and the rest of the group becomes his bodyguards/underlings.

Well then how does Vader still miss Leia? Luke reaches out to Leia and Leia uses the Force to locate Luke. Though she doesn't realize she's doing that. But if we consider the range at which Leia was away when Luke reached out to her, and the sheer size of Cloud City I think Leia's use of the Force would qualify as a massive amount of Force power. Leia should have pinged on Vader's radar if she was using the Force as he would have been close enough to sense her being that if Luke could reach her and she reach him through the Force then Vader's proximity to Cloud city during this scene should make him close enough.

Aside from just plot reasons there isn't a real reason why Leia should have escaped Vader's notice in that instance being as how she would have to used to Force in order to find Luke before those Tie fighters caught up with them.

Leia wasn't the one using the force. Luke was. And Vader already knew Luke was a force user.

Luke used the Force to call out to Leia, but Leia had to have used the Force to find Luke. He's on the underside of Cloud city hanging off a random antenna, if she isn't using the Force to locate Luke then how does she find him? It's not like he knows where he is in order to tell her through the Force where to find him.

by feeling the direction of the call.

Putting mechanics aside for a moment I'd just point something out. I think the Inquistors don't answer to Vader, they go straight to the Emporer. If that's the case, it would be in Vader's interests to keep a "force potential" asset under his own control. So if he realizes this commander is such an asset he uses it himself. However if the Inquistion learns of him Vader will most likely sell them out.

Putting mechanics aside for a moment I'd just point something out. I think the Inquistors don't answer to Vader, they go straight to the Emporer. If that's the case, it would be in Vader's interests to keep a "force potential" asset under his own control. So if he realizes this commander is such an asset he uses it himself. However if the Inquistion learns of him Vader will most likely sell them out.

Jossed.

There's an added scene to the beginning of Spark of Rebellion when it aired on ABC that has the Inquisitor reporting directly to Vader, and getting mission orders to "hunt down the children of the Force" specifically from Vader. And at the end of Siege of Lothal, the Emperor commands Vader to send two Inquisitors to hunt down Ahsoka Tano.

Seems pretty clear that the Inquisitorius answers directly to Vader.

That's interesting Donovan! I haven't been all that consistant with my Rebels viewing. I based my thoughts off the new Vader comic from Marvel. I can see where having Vader head the Inquistion does add weight to the whole "Vader hunted down and killed all the Jedi." However the Emperor ordering Vader to send two Inquisitors after Ahsoka could be viewed either way. But yes, Vader clearly has more to do with them than I thought.

Putting mechanics aside for a moment I'd just point something out. I think the Inquistors don't answer to Vader, they go straight to the Emporer. If that's the case, it would be in Vader's interests to keep a "force potential" asset under his own control. So if he realizes this commander is such an asset he uses it himself. However if the Inquistion learns of him Vader will most likely sell them out.

Jossed.

There's an added scene to the beginning of Spark of Rebellion when it aired on ABC that has the Inquisitor reporting directly to Vader, and getting mission orders to "hunt down the children of the Force" specifically from Vader. And at the end of Siege of Lothal, the Emperor commands Vader to send two Inquisitors to hunt down Ahsoka Tano.

Seems pretty clear that the Inquisitorius answers directly to Vader.

I think it's probably misleading to assume that the Inquisitorius reports to the Emperor OR Vader, they're probably both running it, and everyone knows Vader reports the Emperor. It could be that the Emperor assigned a group of Inquisitors to Vader, and he runs the remainder, it's possible that the entire Inquisitorius reports to Vader, it's possible that there's a High Inquisitor (a la Tremayne) that all the Inquisitors report to, and the HI reports to Vader or the HI reports to the Emperor and still obeys Vader... etc, etc, etc.

In both the examples above, it could be that the Emperor just felt like delegating the details to Vader.

Point being, it's all supposition, so nothing about the Inquisitors' command structure really qualify as "clear" to any degree.

Right now, based on the information we have available, the Inquisitors are shown to report to Vader. As noted, there's direct scenes where the Inquisitor reports directly to Darth Vader. Palps is more like the Commander-in-Chief, in that while all the armed forces of the Empire do report to him, in terms of practicality only the most high-ranking members of the Imperial military report directly to the Emperor, with everyone else reporting to a direct superior, much like we saw the Death Star command staff reporting to Tarkin in ANH, or various Imperial officers aboard the Executor reporting to Ozzel/Piett who then relayed that info to Vader.

Now come Season 2 of Rebels, we may find out more of the Inquisitorius that changes that, but if one's concerned with how it shakes out in canon, then the Inquisitors report to Vader.

That being said, if for one's campaign the GM wants to have the Inquisitors report to a spice-addled Kowakian Monkey-Lizard that's the real power behind the Empire and that Palps is just an old-school Disney animatronic, they're certainly free to do that. It's not canon, but if it works for that GM's campaign, then go with it.

Also keep in mind that on film, sensing the Force in someone usually requires some form of confirmation. The initial ping is "there is something strange about that one" and then they have to be watched before they know for sure.

That leads me to believe that there are some that there are some false positives on that initial read, maybe individuals who are stronger than average with the Force, but not so much that they are "Force Sensitive" or some who are sensitive, but that is the extent of their potential.

Confirmations mostly seem to be obvious examples of using the Force. Sensing it in others creates a lead rather than proof.

It's possible that the Inquisitors report to Vader in the Rebels timeline, but not later on after Episode IV. I've been reading the Star Wars and Darth Vader comics, and it's pretty clear that Vader is not currently in charge of the Inquisitors post-Death Star.

This is a strange case where we have two canonical sources covering the same character, in two different time periods, running concurrently. But I think it's safe to say that in the post-Death Star/pre-ESB continuity, Vader is not currently overseeing the Empire's Inquisitors.

It's worth noting that Vader is also not in good standing with the Emperor in the Darth Vader comics

It's possible that the Inquisitors report to Vader in the Rebels timeline, but not later on after Episode IV. I've been reading the Star Wars and Darth Vader comics, and it's pretty clear that Vader is not currently in charge of the Inquisitors post-Death Star.

Actually, are the Inquisitors still around by the time Darth Vader happens? There's been no sign of them, and while they might have been shifted to Palpatine's direct command, I might believe that Rebels builds up to the destruction of the Inquisitorius as an organization.

It's possible that the Inquisitors report to Vader in the Rebels timeline, but not later on after Episode IV. I've been reading the Star Wars and Darth Vader comics, and it's pretty clear that Vader is not currently in charge of the Inquisitors post-Death Star.

Actually, are the Inquisitors still around by the time Darth Vader happens? There's been no sign of them, and while they might have been shifted to Palpatine's direct command, I might believe that Rebels builds up to the destruction of the Inquisitorius as an organization.

I may be wrong, but I think there was a very brief mention of an inquisitor in the series. Since they are not tasked with pursuing the main group of rebels (Luke, Leia, Han, etc), it's not unusual that they haven't been featured; in fact, it could be important to the upcoming movies that the main characters not be aware of them until later. They are a secret organization, after all!

It's worth noting that Vader is also not in good standing with the Emperor in the Darth Vader comics

Yeah, one of the (several) things I don't like about that comic line. It's not that they wouldn't butt heads or have their own agendas, but it's just presented in such a childish manner. Lords of the Sith, for all its faults, handled it better.

I have a premonition what is going to happen if my Jedi character is ever being chased by Vader and uses Shroud.

Oh well, what's 30 wasted XP

As has been mentioned, the more someone uses the Force, and the greater the effect of that use, the easier it is to sense a disturbance in the Force. Unless your guy has been going around, crushing planets with his Force abilities, he may not 'show up' to Vader as a Force user. But that doesn't mean you can't make the poor guy sweat a bit. "Darth Vader paces in front of your group, the hollow sound of his breathing apparatus hissing as he speaks, 'You will find the ​Millennium Falcon and return it and its crew and passengers to me. Failure will result in my...disappointment. Do I make myself clear?' Without waiting for an answer, he turns and strides out of the room. As he reaches the door, he suddenly stops, his head turning slightly, as if he were about to turn around and face you again. After an agonizingly long moment, he turns and walks out the door, but not as quickly as before. What do you do?"

I have a premonition what is going to happen if my Jedi character is ever being chased by Vader and uses Shroud.

Oh well, what's 30 wasted XP

I have similar experience with another PC that my rogue force user is training. His main intention is to use him as a force blank to blind side any inquisitors we may encounter in future. It's rare to have a non-jedi apprentice and master working together, but in a hostile galaxy with both being like minded slicers, hiest masters, the arrangement works.

Now, if only he knew Tobin's master was a sith lightsaber.

I think the two best answers in this thread have been that it depends on actively using the Force and that it depends on "plot". The thing is, these aren't necessarily separate answers because a thing that exists in the Star Wars universe is the living and cosmic Force. I struggle to remember which is which but regardless, this is a universe where there is a chosen one (if it's not just Jedi superstition), and pivotal moments and people that shape the universe. Remember it's not always a case of detecting the Force user, it's often the case of sensing a "disturbance in the Force". When a young not-yet-jedi from some backwater planet shows up in an X-Wing to destroy the Death Star, that's not just a use of the Force you can sense, it's a rock dropped in a still lake, it's a branch point in history rushing towards you, it's the pressure before the storm. It's all of these. SOme people are saying "it happens when it's appropriate to the plot", but "the plot" in Star Wars is an in-Universe thing. The final fatal conclusion of the relationship between Vader and Obi Wan? How could either of them not feel that? Vader walks down a street whilst in a building not far away and novice Force user who will spend his life hiding on this planet moves a rock back around the room with his mind. Maybe Vader gets a prickling sensation, but it is faint and he walks on.

So I think both of these are good answers in a way. It's about use of your powers but it's also about destiny. If you want to be evil, base it on how many Destiny Points they have spent.

I don't think it's been mentioned yet but just because you are Force Sensitive doesn't mean you are a Jedi. Many people are Force Sensitive and if Empire went after them all there would be even more Rebellion. As long as that Force Sensitive doesn't start using the Force in front of Vader, I doubt he would give a drek. Even if he did sense the character's use of the force in small ways, it's not the same as if they started to throw crates around with the Move power or whipped out a lightsaber and started hacking off limbs. That's when he's going open up that can of space-worms.

I don't think it's been mentioned yet but just because you are Force Sensitive doesn't mean you are a Jedi. Many people are Force Sensitive and if Empire went after them all there would be even more Rebellion. As long as that Force Sensitive doesn't start using the Force in front of Vader, I doubt he would give a drek. Even if he did sense the character's use of the force in small ways, it's not the same as if they started to throw crates around with the Move power or whipped out a lightsaber and started hacking off limbs. That's when he's going open up that can of space-worms.

Good point.

Granted this is going mostly by Legends, but Palps (and by extension the Empire) generally seemed to be of three camps when it came to Force users.

Camp #1) As long as they're not using their powers and obeying Imperial law, leave them alone.

Camp #2) If they're using their powers and are on the Imperial payroll, let them do their thing.

Camp #3) If they're using their powers to openly resist the Empire, crush them like bugs.

Kanan managed to survive after Order 66 for so long by keeping a very low profile and not using his Force abilities (and being a bit of a lecherous drunkard if A New Dawn is any indication). Luke had always been Force-sensitive, but he never really started developing his abilities until after he met Obi-Wan, so again he flew under the radar. Same with Ezra, whose Force abilities were in the nascent/reflexive stage until he met up with the crew of the Ghost and Kanan decided to train the boy.

Obi-Wan was something of a curious case, from what Legends had to suggest, Palps didn't care quite so much about the old Jedi so long as Kenobi kept his head down and wasn't actively spurring dissent or leading an open resistance; heck Palps may have even hoped that Kenobi would take another apprentice and screw it up as badly as he'd done with Anakin, providing Sidious with another dark side asset. Vader was the one focused on Kenobi, likely out of a burning need to avenge his maiming at Mustafar. Again, Legends, but the excellent book Dark Lord, The Rise of Darth Vader (set shortly after RotS) expands in this. Vader was the one that was gung-ho to hunt down and destroy every single surviving Jedi out there, while Palps was content with the Order being crushed and that any survivors would be forced to hide with few if any major allies (given they'd been scapegoated as being responsible for the Clone Wars as a power play to seize control of the government), thus making them not much of a threat to his Galactic Empire.