Answer: whistles

AnswerCrossword Clue
WHISTLESReferees' needs
WHISTLESTrain warnings
WHISTLESSounds from a teakettle
WHISTLESEmulates a teapot
whistlesdevice for making such sounds
whistlesto make a high clear sound with breath, air, or steam
whistlesthe sound of whistling
whistlesWHISTLE, to make a shrill sound