meaning of the word `triangle`

Would you explain me please…

I can`t understand the meaning of the word `triangle`here in the sentence: `When the triangle sounded in the morning,Judy dressed more quickly even than usual`

Hello!

 There is a musical instrument called triangle. It could refer to that:)

 My opinion:)

This is probably a triangular metal gong that is rung at ranches and camp sites.

The passage above is from John Stainbeck's The Long Valley.

http://womblesrants.blogspot.com/2006/08/bushmoot.html

This gong is also used in plantations for "mustering" labor in the morning.

http://dictionary.cambridge.org/define.asp?dict=CALD&key=52657&ph=on

  Thanks a lot for the explanation.I think you are all right.

Usually these triangle music instruments are used by very young people in their music bands. Maybe, adults also use them.

http://en.wikipedia.org/wiki/File:Angelika_Kauffmann_Allegra.jpg

http://en.wikipedia.org/wiki/Triangle_(instrument)

So do I.

 I am a pass-by!