Cipher Slider

As an action, you may blow this whistle. You
may blow a musical note or choose to make a
DC10 performance check. If successful, you can
magically transmit a simple 1 word message, such
as yes, no, safe, danger, stop, or go. On a failure,
you transmit the opposite message. Only those
creatures you specify within 300 ft will hear it.
In a coordinated stealth operation where timely
communication is key, a telepathic whistle is a big step
up from hand signals.