In the Star Trek: Voyager episode "Resolutions," how did two Vidiian ships sneak up on Voyager without them being picked up on sensors?
Do they have cloaking technology? This seems unlikely as they don't even have transporters, replicators, or holo technology. But it's possible.
Did they sneak up on them some other way?
There's no in-universe evidence that the Vidiians have cloaking tech, however they do have a tendency of turning up at inconvenient moments by charging in at warp, then crash-stopping almost on top of their intended victims, a strategy they used to great effect in VOY: Deadlock.
In Resolutions, Voyager has traveled to the designated location and is waiting for the Vidiians to arrive.
DENARA: Of course. Our captain said we could rendezvous with you. He's transmitted the coordinates.
KIM: I have them, sir.
Shortly afterwards, the Vidiians arrive. Kim detects them on short-range sensors as they enter range but evidently didn't see them before that. It seems possible (if not downright likely) that the Vidiian captain intentionally chose that location to prevent Voyager's long-range sensors from detecting the ambush until it was almost too late:
KIM: Got something. Vidiian ship, bearing three two five mark five.
TUVOK: Hail them.
KIM: They aren't responding. Trying on alternating frequencies.
PARIS: I'm reading a second ship, one seven seven mark five.
KIM: I've got it. Now a third.
PARIS: They're surrounding us!
