With this option our users have the comfort of knowing they have a useful safety or communication tool at all times. All outdoors enthusiasts know the value of packing a whistle but seldom follow through with such advice. Now with this attached to your Bino harness it's there when you need it. In some situations it's better to communicate with a soft blow of your whistle rather than yelling or keying a radio to communicate which can give your presence away. No batteries needed is a plus when the chips are down and help is needed.