A device in Mato's Lab, first appearing in [The Midori Arc - Part 1 - A Matter of Honor]].  It resembles an airport weapons detector.  It is a device that measures a person's malicent level, which can be used to determine how evil someone is.  The average person has a level of 12.  In addition to the reading, the geiger offers an insightful and/or humorous comment on the person.