Anakin_the_Hutt
Jedi Master
VADER: HE is here.
TARKIN: Obi-Wan Kenobi? What makes you think so?
VADER: A tremor in the Force. The last time I felt it, was in the presence of my old Master.
People give off particular VIBES in the Force. Kinda like, fingerprints. Vader can feel when Obi-Wan is near. Vader probably sensed Luke, too - but Obi-Wan's vibes would've been enough for him to put the station on high alert.
During the Death Star trench, Vader sensed that the Force was strong in whoever it was he was chasing. That wasn't a 'By the Balls of the Force - he's good!" moment. He was LITERALLY commenting, "The Force is strong in this one."
If you're soley going by the movies - how else do you explain Palpatine's exchange with Vader in ESB?
Palpatine alerts Vader of a disturbance in the Force, but Vader says he already felt it.
Palpatine says the disturbance is the guy who blew up the Death Star, who happens to be Vader's son. Vader plays dumb, but Palpatine insists he knows Vader already knows all of this.
Vader then dismisses Luke as worthless since Obi-Wan is dead. But Palpatine KNOWS Vader wants Luke for himself. (even the OPENING CRAWL says Vader is obsessed with finding Luke)
It's when Palpatine says Luke must die because the Force is strong in him, that Vader offers Luke to his Master. The only way to postpone his death.
VADER: What is thy bidding, my Master?
PALPATINE: There is a great disturbance in the Force.
VADER: I have felt it.
PALPATINE: We have a new enemy...the young Rebel who destroyed the Death Star. I have no doubt that this boy is the offspring of Anakin Skywalker.
VADER: How is that possible?
PALPATINE: Search your feelings, Lord Vader. You will know it to be true. He could destroy us.
VADER: He's just a boy. Obi-Wan can no longer help him.
PALPATINE: The Force is strong with him. The son of Skywalker must not become a Jedi.
VADER: If he could be turned, he will become a powerful ally.
PALPATINE: Yes, he will be a great assett. Can it be done?
VADER: He will join us or die, Master