Ring | Studio Ghibli | Howl's Moving Castle | Sophie

Howl's Ring is a magical object that appears in the movie adaptation of Howl's Moving Castle. It holds a connection to Howl's heart within Calcifer. Calling out to Calcifer causes the small stone on it to emit a beam of light pointing in his direction. It appears as a dark metal band with a small stone and several runes.

Howl gives a similar ring to Sophie, placing it on her index finger before she goes out to the palace posing as his mother. He tells her that it guarantees her safe return, however doesn't have much faith in his words. Nearer to the end of the film, the ring emits a blue light instead of red, which leads Sophie to a doorway into Howl's childhood where she finds out how to save him.

(from Howl's Moving Castle Wiki)