Magical Objects - Detectors

Foe-glass

A Foe-glass is a mirror that detects and shows its owner's enemies in or out of focus, depending on how close they are. However, like all Dark detectors, it can be fooled, as mentioned by Harry in the fifth book at the beginning of the first D.A. meeting. Moody, actually Barty Crouch Jr in disguise, claimed that when the figures are most focused, they are the nearest.

Until the debate over Severus Snape's allegiance was resolved in Deathly Hallows, a key argument for those who believed that Snape was still in league with the Order of the Phoenix was the fact that Snape appeared as an enemy in the Foe-glass of Barty Crouch, Jr. in the fourth book (an event that would not have occurred were Snape working for the Death Eaters).

Probity Probe

A Probity Probe detects spells of concealment and hidden magical objects. The detector made its first appearance in Order of the Phoenix as thin and golden in colour. After Voldemort's return, Probes are used as part of the increased security at Gringotts. They are last seen when Harry, Ron, and Hermione arrive at Gringotts to rob the bank of one of Voldemort's Horcruxes.

Remembrall

A Remembrall is a small, clear orb, containing smoke that turns red when detecting that the user has forgotten something. Unfortunately, it does not tell the user what he/she has forgotten which makes it somewhat worthless. The very forgetful Neville is given a Remembrall in Philosopher's Stone, but loses it by his fifth year. Their use is forbidden during the O.W.L. exams, because students can tell if they wrote a wrong answer.

Revealer

A Revealer is a bright red eraser, used to make invisible ink appear. It makes its first appearance in Chamber of Secrets when Hermione tries to make something appear in Tom Riddle's diary.

Secrecy Sensor

The Secrecy Sensor is a dark detector which makes its first appearance when Harry enters Moody's office. The sensor is described as "an object that looked something like an extra-squiggly, golden television aerial." It vibrates when it detects concealment and lies. Moody mentions that it is, "No use here of course, too much interference--students in every direction lying about why they haven't done their homework." However, it may be that this was due to the sinister intentions of Moody (actually Barty Crouch Jr.).

In Order of the Phoenix, it is shown that Secrecy Sensors are used at the Atrium Desk in the Ministry of Magic upon visitor to the government locale. Later in the book, Harry mentions that they can be easily fooled like its other dark-detecting counterparts. In Half-Blood Prince, due to Hogwarts's new stringent security measures, Argus Filch is assigned to run every student entering the castle with Secrecy Sensors. All the owls flying into Hogwarts, too, are placed under his measure to detect that no Dark object enters the castle through mail. Later, Hermione explains that though Secrecy Sensors detect jinxes, curses, and concealment charms, they cannot detect love potions (because they are not dark, though Harry considers them to be).

Sneakoscope

A Sneakoscope serves as a Dark Arts detector. The device is described as a miniature glass-spinning top that emits shrill noises in the presence of deception. For instance, when an untrustworthy person is near or when a deceitful event takes place nearby.

Sneakoscopes are introduced in Prisoner of Azkaban when Harry receives one from Ron for his 13th birthday. The sneakoscope appears again on the Hogwarts Express, and again up in Harry and Ron's dormitory. Harry later discovers that Scabbers, Ron's rat, who was present each time the Sneakoscope was spinning, is actually a traitorous Animagus named Peter Pettigrew. In Goblet of Fire, the somewhat paranoid Moody has several sneakoscopes that he somehow disabled (possibly related to a crack it was described as having), claiming, "It wouldn't stop whistling." However, it was later revealed that Mad-Eye was really Barty Crouch Jr under the effects of the Polyjuice Potion, thus explaining the constant alerts in his presence. Finally in Deathly Hallows, Hermione gives Harry a Sneakoscope for his seventeenth birthday which they later use to help as a lookout while in hiding.

Weasley Family Clock

The Weasley family has a special clock in their home, the Burrow, with nine hands, one for every member of the family. Instead of telling the time, the clock reveals the location or status of each family member. The known locations are: Home, School, Work, Travelling, Lost, Hospital, Prison, and Mortal Peril. The Weasleys are the only family mentioned to own such a clock. Albus Dumbledore calls the clock "wonderful" and seems impressed by it, suggesting that it's an extremely powerful object.

Only the location of mortal peril is known on the round clock (it is situated where the numeral 12 would normally be). Throughout the first five books, the hands change to reflect the varying statuses of the family members, but by the sixth book, all nine hands point to mortal peril at all times, except when someone is travelling. Mrs. Weasley takes this to mean that, with Voldemort having returned, everyone is always in mortal peril, but she can not verify this, because she does not know anyone else who has a clock like hers.[HP6]

In the 4th book (Harry Potter and the Goblet of Fire) it is mentioned that the clock is a grandfather clock, whereas in the 6th book (Harry Potter and the Half Blood Prince) Mrs. Weasley is able to carry the clock with her and balance it on a stack of laundry.