|Muggles' Guide to Harry Potter - Magic|
|Features||Detects concealment and deceit|
|First Appearance||Harry Potter and the Half-Blood Prince|
Probity Probes are long, silvery probes that allow the bearer to detect concealment and deception: for instance, a Probity Probe would detect use of Polyjuice Potion to disguise oneself, and presumably would detect someone under an Invisibility Cloak.
We first hear of Probity Probes when Harry is preparing for his sixth year at Hogwarts. Bill, who works at Gringotts, hands Harry a money bag, saying that he's gotten some cash for Harry; everyone going into Gringotts now has to pass people with Probity Probes, and entrance to the bank can take several hours.
When Harry, Hermione, Ron, and Griphook enter Gringotts in Harry Potter and the Deathly Hallows to open Bellatrix' vault, there are two wizards with Probity Probes by the door. Harry, from under his Invisibility Cloak, Confunds them so they will not scan Hermione, who is in disguise.
The principles behind a Probity Probe, a Secrecy Sensor, and the part of the Marauder's Map that determines the name of an individual, must be related, however their operation is clearly somewhat different. Secrecy Sensors, as described in the related article, are designed to detect curses, jinxes, and concealment charms, while Probity Probes are apparently designed to detect concealment and deception, but do not, presumably, trigger on jinxes and curses. The Marauders' Map, on the other hand, created by a group of very powerful, young wizards, likely identifies people correctly more or less by accident; the Marauders, wanting the map to be able to display the location of wandering prefects and professors, likely simply embedded an identification charm in the map, not realizing until after they had done so that the charm they had used, possibly stolen from the Restricted section of the library, was powerful enough to pierce Invisibility Cloaks and the Animagus transform.
The name of this artifact is apparently the author playing with words. "Probity probes" sounds somewhat infantile as a name, unless you realize that "probity" is a somewhat archaic word meaning "the quality of having strong moral principles; honesty and decency." As such, a Probity Probe would presumably measure your honesty, moral principles and decency being somewhat harder to quantify.
Like Secrecy Sensors, it is important to the realism of the Wizarding world that probity probes have limitations; rather than checking for any sort of threat, they are limited in what they can detect. Unfortunately, what they can detect is exactly what the Trio must use to get into Gringotts. It is almost to be expected that something like this would be used at Gringotts, as the Wizarding world becomes less secure. It is necessary, though, that the Trio pass them without raising suspicion. Harry chooses to attack the human behind the probe, as being the most obvious weak point of the security system. It is perhaps of interest that many current computer virus infections actually depend on "social engineering," convincing the human operator of the computer system to bypass its protective mechanisms; this is similar to what Harry is doing, though in the Muggle world, the Confundus charm is surprisingly often not needed.