Doctor Doom developed this non-portable device and installed it within Castle Doom. It could be used in an individual interrogation, where a semi-conscious victim would be unable to answer but the truth, in a slow voice. It could also be used to take over the minds of a small group of distracted people for a limited time. Doom used it twice in a quick succession: First, when a woman looking like Doom's old flame Valeria appeared at Doom's door, Doom was suspicious and submitted her to the machine, to discover that she was a spy for Doom's enemy Rudolfo Fortunov. Rudolfo indeed wanted Doom to discover this, for it would have a psychological effect on him, and because he expected the chivalrous Doom to not punish the spy because of that. The spy then sabotaged Castle Doom's defenses, allowing for Rudolfo and his troops to invade it (although Rudolfo sent a robot impersonator in his place via remote control). Doom then used a Hologram Projector and one Doombot to keep Rudolfo and some of his men busy with a skirmish, while he directed the Hypno-Probe against them, taking control of their minds.
The story does not specify whether the Hypno-Probe controlled the mind of the robot Rudolfo, preventing it from moving; or the mind of the real Rudolfo, who was using a remote control to handle the robot and, likely, was using a monitor to see whatever the robot was seeing.