A whistling tea kettle is a stove top kettle that uses the steam to make it whistle which will let you know when your water is hot.(Note: some electric kettles have a whistle feature)
Best applications that require boiling water like black tea, instant coffee, instant soups or hot cereals etc. then a whistling tea kettle is your best option because of the simplicity of how it works and ease of care also you can be doing other things while the water is heating up and when it begins to boil the kettle will give a whistle to let you know it’s ready.
Whistling teakettles come in many shapes and sizes and materials most common sizes are small to eight cup water capacity and construction materials range from stainless steel, copper, glass and cast iron.
Most stovetop whistling kettles are much easier to use than an electric tea kettle that have a wider range of uses do to the control of the water temperature etc but with a stovetop whistling tea kettle you definitely cannot beat the simplicity in design and ease of use that still gives a variety of uses in the kitchen while keeping the number of cookware items to a minimum.
http://www.tested.com/science/458806-research-finally-shows-why-and-how-tea-kettles-whistle/