I'm not a big fan of the concept that Psi talent can be detected electronically; seems too clinical. I've always treated Psi talent IMTU sort of like in "The Shining" where only other Psi's can really determine talent in another without actually witnessing some sort of psionic manifestation on the part of the user. So, in order for the 3I to detect and monitor the activity of Psi's, they have to have a few of their own and those are on a tight leash.
So, being a big fan of B5, I borrowed the Psi Cops, sprinkled in a little Darth Vader, and got a squad of Psi working for the Ministry of Intelligence who prowl the Marches invading others' minds and privacy for the safety of the Imperium. A lucky Psi will see them by their aura long before they are seen, if only because they project a red sphere around them like the Super Dome. But a Psi on the run projects a unique aura of their own, making them easy to track. So once they get you, and they always get you, they psionically break down any defenses you have and rummage through your mind like a box of old photos, looking for signs of Zhodani influence. If they don't find any and you pass a genetic test for any Zhondai markers, you may be recruited, allowed to take debilitating anti-psi drugs for the rest of your life, or maybe just lobotomized and left in a nice, quiet ward in some out of the way hospital. Sinister, but it's for the greater good of the 3I, right?