Sure, sure, you think looking for an intermix chamber of antimatter and matter that is not 1:1 is easy. What happens if they are simply leaking plasma from their nacelles? Or what if the ship is trying to steal your tech by luring an engineer onboard to repair “damaged” systems?
Or what if their warp drive uses an artificial singularity?
Then why did a hologram of Janeway tell a bunch of kids she once was a salamander?