Nightsong

A language of high-pitched whistles produced by an instrument similar to a dog whistle. Humans can't hear it, making it very useful for conveying information vampires don't want humans to overhear.  The whistles used to produce it were traditionally made from human bones, although more recent ones are made from metal to produce a more consistent sound with far less effort.  This whistle has 2 finger holes and can play 3 notes.  Each phrase has a specific combination of pitch and length of notes played in it, and vocabulary is limited.

Writing System

Nightsong is rarely written, but when it is, it's written in a similar manner to morse code with dots and dashes of varying length.  The height of a dot or dash in a line indicates it's pitch, and the length of the dash represents how many beats it is.

Vocabulary

Most phrases consist of 5 notes or less.  A low note played for four beats or more is both a plea for help, and a reply to it. To keep hands free, danger callouts are all done with low notes, for instance 2 short low notes means 'Hunter'. 'med low low high', all one beat is a greeting.