Psychic boosters are protoss communication devices built into vessels such as carriers. It is through these that protoss commanders can send telepathic messages on a wide scale in a manner similar to a terran radio, able to sense the recipients' reaction(s) to his/her message. It appears that portable psychic boosters exist also, carried by protoss commanders when not aboard their flagship. These devices can send messages throughout an entire fleet simultaneously and cannot be intercepted by enemy forces.