No need to worry, Smurf! They refer to it as the alethiometer in the film.
(Hijacked from the film's IMDB page)
[from Trailer]
Lyra Belacqua: [upon receiving the alethiometer] What is this?
Master of Jordan: It's an alethiometer. It tells the truth. You are meant to have it. You keep the alethiometer to yourself, it's of the utmost importance to yourself, to all of us, and perhaps to all creation.
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