Secrecy Sensor

• Type: Dark Detector, Magical Device
• Owners: Alastor Moody (impersonated by Barty Crouch Jr.), Ministry of Magic, Hogwarts School of Witchcraft and Wizardry
• Maker: Unknown

A Secrecy Sensor is a magical instrument designed to detect concealment and untruths. Its appearance is not standardized and has been described in at least two distinct forms. The model kept by Alastor Moody in his Defence Against the Dark Arts office at Hogwarts resembled a “very crooked, golden television aerial.” It was one of several Dark Detectors he possessed, alongside a Foe-Glass and a Sneakoscope. A different model was used by the Ministry of Magic for security at their visitor's entrance. This version was described as a “long, thin golden rod with a number of complicated knobs on it.”

The primary function of a Secrecy Sensor is to alert its user to the presence of lies and concealment. When it detects such activity, it vibrates and hums, acting as an alarm. However, the device has limitations. Older or less refined models can be “over-sensitive,” making them impractical in locations with a high concentration of minor secrets. Barty Crouch Jr., while disguised as Alastor Moody, claimed his sensor was constantly “going haywire” because students were telling trivial lies, such as fibbing about homework. This constant activity provided perfect cover for his own significant deceptions as an impostor in the school. The Ministry of Magic upgraded their sensors for this reason. The newer model used by the watch-wizard at the Ministry entrance in 1995 seemed more precise. It was used to physically scan visitors upon entry to detect any hidden Dark Magic or ill intent. Later, when Hogwarts security was increased following the death of Albus Dumbledore, Argus Filch used a Secrecy Sensor to check students leaving the Hogwarts Express. He prodded Ron Weasley with it, and upon Ron identifying an object as a Ton-Tongue Toffee, Filch seemed satisfied, suggesting the sensor can help verify if an item is what it is claimed to be, or at least confirm that it is not a Dark Object.

The Secrecy Sensor is a known tool used by both Aurors and the Ministry of Magic as a standard piece of security and detection equipment. In the 1994-1995 school year, Barty Crouch Jr. brought one to Hogwarts while impersonating Alastor Moody. He used the excuse of its over-sensitivity to deflect any suspicion from himself. By August 1995, the Ministry of Magic had employed a newer model at its London headquarters, as the one previously in use was deemed too sensitive for practical application. Harry Potter was scanned by one of these devices when he attended his disciplinary hearing. In June 1997, after Lord Voldemort's return was made public and Hogwarts fell under Ministry influence, Secrecy Sensors were used by staff like Argus Filch to screen students and their possessions.

The Secrecy Sensor is first introduced to establish the vigilant and paranoid character of “Mad-Eye” Moody. Its presence serves as a point of dramatic irony, as the man employing it to detect deceit is himself a complete impostor. Crouch Jr.'s clever manipulation of the device's known flaw highlights his cunning and allows him to operate undetected. The sensor's later appearances at the Ministry of Magic and Hogwarts serve as a barometer for the rising tension and suspicion in the wizarding world. It symbolizes the authorities' attempts to impose order and security in the face of growing threats from Lord Voldemort and his Death Eaters.

In the film adaptation of Harry Potter and the Goblet of Fire, Moody's office is filled with various magical detectors, but the Secrecy Sensor is not specifically identified or described as it is in the novel. (film)