Harry Potter: "What's that?"
Professor Moody: "Secrecy Sensor. Vibrates when it detects concealment and lies... no use here, of course, too much interference—students in every direction lying about why they haven't done their homework."
Bartemius Crouch Junior disguised as Alastor Moody explaining his Secrecy Sensor to Harry Potter[src]

A Secrecy Sensor is a type of Dark Detector. It is shaped like an aerial, but it is gold in colour and very squiggly. It vibrates when it detects concealment and lies.



Bartemius Crouch Junior, while disguised as Alastor Moody, had one in his office during the 1994–1995 school year at Hogwarts School of Witchcraft and Wizardry. It was no use to him at the school because it was constantly humming -- he claimed that students were always nearby telling lies about why they had not completed their homework assignments,[2] but it was almost certainly detecting Crouch himself.[3]


When Harry entered the Room of Requirement before the first Dumbledore's Army meeting, he also discovered several secrecy sensors among other Dark Detectors.[4]


Argus Filch using his Secrecy Sensor

During the 1996–1997 school year at Hogwarts, as part of the school's increased security measures, caretaker Argus Filch scanned all students who entered or left the school with a secrecy sensor, in order to detect any dark artefacts that may have been brought into the school.[5][6]

Behind the scenes

  • When Harry first visits the Ministry of Magic in August 1995 the wizard at the security desk checks him over a Secrecy Sensor before letting him enter further into the Ministry.[7]
  • Secrecy Sensors appear vastly different in the Nintendo DS version of Harry Potter and the Deathly Hallows: Part 1. Here, they are areas of light that move along the ground in set patterns, appearing similar in appearance to spotlights. When Harry steps into one, it causes a number of wizards to Apparate to his location and attack. Interestingly, Ron, who is controlled by the game, does not activate the Secrecy Sensors should he step into one. This may be so the player is not attacked due to actions outside his control, or merely an error in programming.


Notes and references

  1. Harry Potter and the Half-Blood Prince, Chapter 15 (The Unbreakable Vow)
  2. Harry Potter and the Goblet of Fire, Chapter 20 (The First Task)
  3. Harry Potter and the Goblet of Fire, Chapter 35 (Veritaserum)
  4. Harry Potter and the Order of the Phoenix, Chapter 18 (Dumbledore's Army)
  5. Harry Potter and the Half-Blood Prince, Chapter 11 (Hermione's Helping Hand)
  6. Harry Potter and the Half-Blood Prince, Chapter 12 (Silver and Opals)
  7. The physical description of a Secrecy Sensor is quite alike that of a Probity Probe, as such we are not sure what was used there.
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