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, in reality Barty Crouch, Jr. in disguise, claimed that when the whites of their eyes are visible, he is in trouble. A Foe-Glass is hanging in the Room of Requirement in Harry Potter and the Order of the Phoenix when Harry uses the Room for D.A. meetings.
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 a pocket-sized version from Ron for his 13th birthday. Bill says that Pocket Sneakoscopes are unreliable, as it lit up and spun at dinner for apparently no reason, but Fred and George had put beetles in his soup without his knowledge. The sneakoscope appears again on the Hogwarts Express, and again in Harry and Ron's dormitory. Harry later discovers that Scabbers, Ron's rat, who is present each time the Sneakoscope is spinning, is actually Peter Pettigrew in Animagus form. 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, Moody was later revealed to actually be 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.
Sneakoscopes are introduced in Prisoner of Azkaban when Harry receives a pocket-sized version from Ron for his 13th birthday. Bill says that Pocket Sneakoscopes are unreliable, as it lit up and spun at dinner for apparently no reason, but Fred and George had put beetles in his soup without his knowledge. The sneakoscope appears again on the Hogwarts Express, and again in Harry and Ron's dormitory. Harry later discovers that Scabbers, Ron's rat, who is present each time the Sneakoscope is spinning, is actually Peter Pettigrew in Animagus form. 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, Moody was later revealed to actually be 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.
The Marauder's Map
The Marauder's Map is a magical map of Hogwarts created by Remus Lupin, Peter Pettigrew, Sirius Black, and James Potter (respectively nicknamed "Moony," "Wormtail," "Padfoot," and "Prongs") while they were students at Hogwarts. During this time, they gained extensive knowledge about the school grounds, such as its various hidden passages, from their frequent night-time adventures together.
In Harry Potter and the Prisoner of Azkaban, Fred and George Weasley give the map to Harry so he can travel to the village of Hogsmeade through a hidden passageway. The twins had previously stolen the map from a drawer in Filch's office that contained dangerous confiscated objects; it is revealed by Lupin that Filch probably knew what it was but not how to work it. Snape later finds the map in Harry's possession and tries to force it to reveal its secrets, but the map merely mocks and insults him. Lupin (one of the creators of the map), the current Defence Against the Dark Arts teacher, is called upon to investigate this "dark object", and confiscates it to keep Harry safe, though he returns it to Harry after resigning his post at Hogwarts. From then on, the map becomes one of Harry's most useful tools in his ongoing adventures.
At first glance, the Map is simply a blank piece of parchment; but when the user points his wand at the Map and says, "I solemnly swear that I am up to no good", the message "Messrs. Moony, Wormtail, Padfoot and Prongs, purveyors of aids to magical mischief-makers, are proud to present the Marauder's Map," and a detailed layout of Hogwarts appears. Saying, "Mischief managed!" while pointing ones wand on the parchment returns the map to its original blank state. The map displays the location of everyone within the castle and its grounds, and includes the location of secret passageways and instructions on how to access them. However, several locations like the Room of Requirement and the Chamber of Secrets do not appear on the map, either because the Marauders did not have any knowledge of them, or, in the case of the former, they are Unplottable. Furthermore, Animagus disguises, Polyjuice Potion, and Invisibility Cloaks cannot fool the map, as shown in Goblet of Fire when Barty Crouch, Jr., using a Polyjuice Potion to disguise himself as Moody, and in Prisoner of Azkaban when Peter Pettigrew, who is supposed to be dead but as an Animagus has transformed into a rat, are both displayed on the map.
On the prop version of the map made for the films, the lines are made up of what at first glance are just random letters, but upon closer inspection are Latin words. The series makes no mention of Harry recovering the map from Moody's office, even though he continued to use it in later books; when asked about this discrepancy, Rowling answered that Harry had indeed sneaked into the office and recovered it in the days following the Third Task, and that she had forgotten to include this detail in the book. When asked during an online question session, "What child did Harry give the Marauder's Map to, if any?" (after his school years), Rowling responded, "I've got a feeling he didn't give it to any of them, but that James (Harry's eldest son) sneaked it out of his father's desk one day."
In Harry Potter and the Prisoner of Azkaban, Fred and George Weasley give the map to Harry so he can travel to the village of Hogsmeade through a hidden passageway. The twins had previously stolen the map from a drawer in Filch's office that contained dangerous confiscated objects; it is revealed by Lupin that Filch probably knew what it was but not how to work it. Snape later finds the map in Harry's possession and tries to force it to reveal its secrets, but the map merely mocks and insults him. Lupin (one of the creators of the map), the current Defence Against the Dark Arts teacher, is called upon to investigate this "dark object", and confiscates it to keep Harry safe, though he returns it to Harry after resigning his post at Hogwarts. From then on, the map becomes one of Harry's most useful tools in his ongoing adventures.
At first glance, the Map is simply a blank piece of parchment; but when the user points his wand at the Map and says, "I solemnly swear that I am up to no good", the message "Messrs. Moony, Wormtail, Padfoot and Prongs, purveyors of aids to magical mischief-makers, are proud to present the Marauder's Map," and a detailed layout of Hogwarts appears. Saying, "Mischief managed!" while pointing ones wand on the parchment returns the map to its original blank state. The map displays the location of everyone within the castle and its grounds, and includes the location of secret passageways and instructions on how to access them. However, several locations like the Room of Requirement and the Chamber of Secrets do not appear on the map, either because the Marauders did not have any knowledge of them, or, in the case of the former, they are Unplottable. Furthermore, Animagus disguises, Polyjuice Potion, and Invisibility Cloaks cannot fool the map, as shown in Goblet of Fire when Barty Crouch, Jr., using a Polyjuice Potion to disguise himself as Moody, and in Prisoner of Azkaban when Peter Pettigrew, who is supposed to be dead but as an Animagus has transformed into a rat, are both displayed on the map.
On the prop version of the map made for the films, the lines are made up of what at first glance are just random letters, but upon closer inspection are Latin words. The series makes no mention of Harry recovering the map from Moody's office, even though he continued to use it in later books; when asked about this discrepancy, Rowling answered that Harry had indeed sneaked into the office and recovered it in the days following the Third Task, and that she had forgotten to include this detail in the book. When asked during an online question session, "What child did Harry give the Marauder's Map to, if any?" (after his school years), Rowling responded, "I've got a feeling he didn't give it to any of them, but that James (Harry's eldest son) sneaked it out of his father's desk one day."
Remembrall
A Remembrall is a small, clear orb, about the size of a tennis ball, containing smoke that turns red when it detects that the person holding it has forgotten something. Unfortunately, it does not tell the holder what he/she has forgotten which makes it somewhat worthless. The forgetful Neville Longbottom is sent a Remembrall by his grandmother in Philosopher's Stone. Draco Malfoy later steals and throws it during flying lessons, causing Harry to pursue it on his broomstick and catch it inches from McGonagall's window. This first example of Harry's prowess on a broomstick earns him the position of Seeker on the Gryffindor Quidditch squad. Remembralls are forbidden from being used during the O.W.L. exams, as they would enable students to know if they had written a wrong answer.
Probity Probe
A Probity Probe detects spells of concealment and hidden magical objects. The detector made its first appearance in Order of the Phoenix at the Ministry of Magic as a thin golden rod. After Voldemort's return, Probes are used as part of the increased security at Gringotts as well as for scanning the students of Hogwarts for Dark objects. They are last seen when Harry, Ron, and Hermione arrive at Gringotts in The Deathly Hallows to rob Bellatrix Lestrange's vault of one of Voldemort's Horcruxes.
Secrecy Sensor
The Secrecy Sensor is a dark detector described as "an object that looked something like an extra-squiggly, golden television aerial." It vibrates when it detects concealment and lies. In Harry Potter and the Goblet of Fire, 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 is because Moody was actually Barty Crouch, Jr. using Polyjuice Potion.
In Order of the Phoenix, it is shown that Secrecy Sensors are used at the Atrium Desk in the Ministry of Magic upon visitors to the government locale. Later in the book, Harry mentions to Dumbledore's Army that they can be easily fooled like their other dark-detecting counterparts. In Half-Blood Prince, due to Hogwarts' new stringent security measures, Argus Filch is assigned to inspect every student entering the castle with Secrecy Sensors. All the owls flying into Hogwarts, too, are placed under this measure to ensure that no Dark object enters the castle through mail. Later, Hermione explains that although Secrecy Sensors detect jinxes, curses, and Concealment Charms, they cannot detect love potions, as they are not considered Dark.
In Order of the Phoenix, it is shown that Secrecy Sensors are used at the Atrium Desk in the Ministry of Magic upon visitors to the government locale. Later in the book, Harry mentions to Dumbledore's Army that they can be easily fooled like their other dark-detecting counterparts. In Half-Blood Prince, due to Hogwarts' new stringent security measures, Argus Filch is assigned to inspect every student entering the castle with Secrecy Sensors. All the owls flying into Hogwarts, too, are placed under this measure to ensure that no Dark object enters the castle through mail. Later, Hermione explains that although Secrecy Sensors detect jinxes, curses, and Concealment Charms, they cannot detect love potions, as they are not considered Dark.