Lenz trailing the Chinese women
the most fearsome surveillance got carried out by unlikely-looking people that followed you by walking in front of you with small mirrors in their glasses’ temples or elaborate systems of cellular communicators for reporting to the Command Center—or else also by helicopters, also, that flew too high to see, hovering, the tiny chop of their rotors disguised as your own drumming heart.
Context
The screen's catch, inside Lenz's cocaine-paranoid stalk: mirrors as covert surveillance instruments — trackers who follow "by walking in front of you" with temple-mounted mirrors, optics that reverse the direction of watching. That reversal is the scene's whole engine: Lenz first reads the Chinese women as tailing him, then decides "just who had the controlling discretion" and becomes the surveillant himself ("no idea he was back there surveilling them"). The second term here reads "cellular communicators," not "ceiling mirrors." Lenz's auto-darkening tortoise-shell glasses (they darken under each streetlight and lag lightening again, taking out "no less than two of Lenz's vital sensory street-senses," pp. 717-719) are another lens-apparatus in the same family.