Mental Block
Special circuitry in the armor, along with Ross's wristwatch, block against mental takeover in the form of a specially developed mental feedback pulse projected outside the suit and from the watch's internal components; while this pulse is designed to emit when a certain psionic frequency registered as 'hostile' (basically any psionic frequency) begins to effect the wearer, more subtle use of psionics can avoid the defenses. These have yet to be 100% effective or tested in a controlled environment.