Hypno Trinket

30. I will refuse all gifts from the Evil Overlord. They probably contain mind-control devices that would make me giddily happy to marry him. It's demeaning enough to be head-over-heels for the Hero, let alone a creep like the EO.

—The Universal Genre Savvy Guide, "The True Love List"

The power to Hypnotize being imbued in a wearable item, by either magic or Applied Phlebotinum. It doesn't matter the form. It's usually just a piece of Jewelry, but it can be anything from a hat to a wedding dress.

Heck, it doesn't always have to be mind control in the typical sense. It can also be a conduit for a spirit to possess the wearer. This can even cause the victim to look like the spirit did in life. Many of these things tend to be Soul Jars of the Sealed Evil in a Can, and are purposely made desirable for this effect.

Note this is direct mind control, not simply corrupting people with the object's dark influence. Also, this apply to items worn by the victim, not by the hypnotizer.

A frequent way to Hypnotize the Princess.

And of course, like most mind control tropes, Rule 34 and Fetish Fuel can apply, especially with Author Appeal.

A Sub-Trope of Mind Control Device.

Compare Artifact of Attraction (rather than hypnotize causes Gold Fever), Clothes Make the Maniac, The Hat Makes the Man, Hypno Ray, Instant Allegiance Artifact, Love Potion, Mirror Morality Machine.

Examples of Hypno Trinket include:

Anime and Manga

Hige's collar and the collars of at least 22 other wolves in Wolfs Rain is a mind-control device of Lady Jagara's.
In an Inu Yasha filler episode, a Chinese boar yokai collects fiancées this way.
Dragon Ball Z: Broly in Movie 8 was given a mind-control crown by his dad (and going by the flashback, it was without his consent), initially to control Broly so as to not have him have outbursts, but shortly thereafter, he ended up used by Paragus to blow up planets—presumably more than before, given the fact that the amount was high enough to get even King Kai to notice.
Arguably, the Red String of Fate that Shampoo uses on Ranma in the Ranma ½ TV series. And then Shampoo just had to brag about it all the time, therefore Akane gets enough time to brew a plan to get it cut...
Digimon Adventure 02 has the Dark Rings (and later, upgraded Dark Spirals.)
Used in Orphen Revenge, when Majik gets Brainwashed and Crazy by Esperanza due to a Nice Hat that she puts on him. Orphen "fixes" him via both both blasting and talking to him, then lowring Majik's defense enough to blast the hat away.

Comic Books

Disney did this with a Chip 'n Dale Rescue Rangers comic, where Gadget and a bunch of other creatures were enslaved with magical necklaces by Fat Cat.

Fan Works

Small silver tags were used in The Man With No Name to gain control over an army's worth of Reavers as well as a few humans.

Film

Dale Arden is given a mind-controlling ring by Ming the Merciless in the Flash Gordon movie.

Literature

In Illusion by Paula Volsky, the king's brother uses hypnotic jewelry to make ladies in the court fall for him when they first spurn his advances.
The Caps in The Tripods.

Live-Action TV

Are You Afraid of the Dark? uses an old riding jacket that causes a girl to be possessed by the spirit of her dead aunt.
Similarly, in The Avengers episode "Return of the Cybernauts", Beresford gives Mrs. Peel a bracelet, which is actually a mind control device.
In The Monkees episode "Monstrous Monkee Mash," the vampiress Lorelei mind-controls her victims with a magic necklace, which she bestows with a kiss. (Prompting the repeated exchange: "What a kiss! I've never felt this way before!" "You fool, it is not my kiss, but the magic necklace!" "What a necklace! I've never felt this way before!" The villainess herself got tired of it...)
In the original The Twilight Zone episode "Dead Man's Shoes", a homeless man finds the body of a gangster's victim, puts on his shoes, and is possessed by the victim. The '80s remake did a gender flip, "Dead Woman's Shoes", in which the trinket is a pair of shoes belonging to the murdered wife of a rich corporate type.
In Merlin, Uther is hypnotized with a magic amulet powered by troll blood.
- Also Gwen and the magic bracelet in "Lancelot Du Lac".
In Smallville, Winslow Schott has a diadem that emits a frequency to the brain stem. He got Courtney Whitmore to commit crimes for him and Lois try to kill Clark (who had his powers at the time).

Tabletop Games

In Warhammer Fantasy Battle, Azhag the Slaughterer has a crown that tries to control him. However, as Azhag is an orc this isn't going that easily, and he suffers from stupidity by the power struggle within.
- Also, in Warhammer Online and related media Grumlok has an enchanted amulet that makes him unwittingly carry out the Witch King's plans. Although later Greenskin quests suggest that he's not entirely mind-controlled...

Gamebooks

In Book 3 of the Lone Wolf series, The Cavern of Kalte, evil sorcerer Vonotar the Traitor uses gold bracelets to control the Ice Barbarians. Putting one on your wrist is a very bad idea.

Video Games

Terra, one of the characters of Final Fantasy VI, wears a slave crown and thus is mind controlled. Cut dialogue that remained in the Data Texts for the game also had Terra shouting "No! Stay Away!" during the procedure from Kefka, implying that she was not a willing participant.
- This gets a Continuity Nod in Dissidia Final Fantasy during the boss fight against her in Onion Knight's storyline. If you check her equipment before the fight, you can see that she is wearing a Hypnocrown to explain why she is acting against her will.
Similar to the Final Fantasy VI example above, in Super Paper Mario, Dimentio implants a floro sprout that he got from the Floro King into Luigi's head when he knocked him unconscious, activating it when betraying Count Bleck so Luigi, or rather, Mr. L, could merge with the Chaos Heart and thus allow him to gain control of it.
The titular item from The Legend of Zelda: Majora's Mask. The evil creature that lives in the mask takes control of any person who puts it on.
There are a couple in Baldur's Gate 2, ranging from cursed items to vitally important devices that used for an interesting subset of Mind Control - mind flayer control. Handy.
This goes back as far as Commander Keen. In the Invasion of the Vorticons trilogy, "The Grand Intellect" enslaves the entire Vorticon race with mind control belts, and it's up to Keen to thwart their invasion and discover who the Grand Intellect really is.
Half-Life mod Point of View assumed that "Alien Slave" critters (the usual and additional varieties) kept enslaved via their prominent collars, and the protagonist loses his to battle damage. Then the second game ran with this - Vortigaunts were revealed to be indeed kept under control this way.

Web Comics

Musaran in the Ciem Webcomic Series is the result of an AI backvisor being attached to the back of Jeraime's head. It essentially makes Jeraime into Arfaas' slave; a no-fee version of the Psycho for Hire.
Magick Chicks has Crystal Skull Dakota used to convince the casual acquaintances that she's a man and mindwipe people who noticed something wrong about her (which happens more often than one could expect, because she's overconfident and not particularly smart). Sometimes this have side effects. In the end, it sort of backfired, because seeing her "Dad" and "Mom" suddenly at each other's throats in the presence of what she was told is a mind control device, Melissa jumped to the obvious conclusion and shattered it, which also broke implanted illusions affecting herself.

Western Animation

In The Legend of Zelda, Ganon puts a necklace on Zelda to force her to marry him.
In Danny Phantom, Johnny 13 uses his girlfriend's clothing to first influence the mind of, and then transfer his girlfriend's soul into, the body of Jazz when she wears them.
An episode of Adventures of Sonic the Hedgehog has Robotnik put a mind-controlling watch on Tails, called a "compliance chip". Robotnik's fatal mistake is putting Scratch and Grounder in command of him.
In Adventure Time, Ice King uses an engagement ring to hypnotize a princess into marrying him.
In Code Lyoko, XANA once manages to sneak an enhanced piece of jewelry to Aelita, who's usually immune to the mind control through his specters, by disguising it as a Valentine's gift from Jérémie.
A literal "love bracelet" was used in an episode of Dinosaucers. Subverted to comic effect when the bracelet ends up on the wrong person. Twice.
The Mad Hatter from Batman the Animated Series controls minds without spirals, using cards marked 10/6 which he sticks on people's heads. And that's just his stock device; he has been known to use other things when appropriate.
The Herculoids episode "Ruler of the Reptons". The Reptons put a crown on Tarra to mind-control her into being their queen.
An episode of Codename: Kids Next Door had a mind-control helmet that was mass-marketed towards girls as a way of controlling their boyfriends. Lizzie put one on Numbuh One, who was forced to take her on a fancy date, until eventually the insane prices made him angry enough to break free.
Kim Possible has Dr. Drakken brainwashing Shego and Kim via this method.
An inversion of the trope was used in The Little Mermaid. When Ursula directly intervened in the goal by disguising herself as Romantic False Lead Vanessa, it's clear that a Hypno Trinket is involved. Said Hypno Trinket (a necklace with a big shell that has Ariel's voice inside), however, was worn by Vanessa—and she uses it to place Prince Eric under mind control. When Ariel's animal friends attack her, they shatter the shell and both free Eric and return Ariel's voice to her.