Ursula's Necklace is an enchanted nautilus shell belonged to the sea witch Ursula who wore it as a necklace and it is an object is featured in Disney's The Little Mermaid.
It was used to capture Ariel's voice as part of the deal to grant her legs. The movie implies that it may be a magical item as it is often glows when Ursula seems to start using a spell such as taking Ariel's voice or even transforming into Vanessa. On a semi-related note, there were also ghostly, seemingly-skeletal hands that originated from the nautilus, as evidenced when Ursula took Ariel's voice as part of the deal.
Close to the end of the movie, at a sailing ship where this false wedding between Vanessa and Prince Eric was held and halted during a sunset, Scuttle snaps the necklace of Vanessa's neck, helped largely by Prince Eric's dog Max when he bit Vanessa on the rump. It falls on the ship's deck and shatters, thus giving Ariel back her voice and freeing Eric from Ursula's spell.
In the Broadway Musical
Although her necklace does not actually appear in the Broadway version of The Little Mermaid, a similar item known as the "Nautilus" was a major plotpoint in it, and it was mentioned that Ursula inherited the nautilus from her father named Poseidon on his deathbed, and with it granted enough power to rule half the sea. It was destroyed by Ariel, and took Ursula with it.
In the Broadway version of the movie, Ariel breaks the necklace which is the source of Ursula's powers.
It's power against the Trident was never stated, but Ursula exclaimed that she would use it to store items.
Disney Princess Magazine
In an issue of Disney Princess magazine, while the necklace is not directly used, several seashells are used to perform a similar feature in capturing the voices of Ariel and her sisters. In capturing the voices, Ursula states that her desire is to have every sweet voice in the sea so she does not have to hear the music.
Ariel manages to defeat Ursula in the end and gives her sisters the enchanted shells, which returns their voices.
This issue also implies that all shells can do this, as King Triton stated, "The sound of the sea is captured in every single shell.".
Ursula's Necklace also appeared in the Kingdom Hearts videogame series in which it appears on Ursula's neck.
In Kingdom Hearts II, the necklace played a major role serving the same purpose as it did in the movie. Ariel gives her voice to Ursula in exchange for legs, and Ursula then uses the voice to hypnotize Eric as Vanessa. In the end, it is the necklace which gives away Vanessa's identity, and in retaliation, Sora uses his Keyblade to destroy it.
- Multiple times during the movie, the necklace will change size between shots. For example, when Ursula transformed into Vanessa, the necklace was big enough for her to cup in both of her hands. In the scene where Vanessa giggles at the necklace, it is small enough for one hand to wrap around it.
- In the game Ariel's Story Studio, the necklace plays the same role as in the movie, only that after the wedding, where the necklace breaks, the necklace reappears again on Ursula's neck, even when she become a giant.
- In the Little Mermaid TV series, Ursula's necklace would often be miscolored. In the episode, "Against the Tide", it was miscolored gray.
- The Necklace made an appearance in the Kingdom Hearts manga.
- In the original fairy tale, the mermaid has her tongue cut off in exchange for legs. In the movie, this was changed to having her voice represented by a glowing yellow orb, most likely to make the scene more gentle for the audience.
- In the original ending of the movie, the necklace is not shattered until after Ursula is defeated.
- In the official comic adaptation of The Little Mermaid, Vanessa is singing in her cabinet without the necklace, implying that she can still use Ariel's voice as long as the necklace is intact.