Listen to the Acme 535 Silent Dog Whistle.  Polished solid brass construction.

The Acme 535 Silent Dog Whistle Polished Brass is not truly "silent", if it were nothing would be able to hear it! The word ‘silent’ is written in inverted commas because you can hear it, BUT only just. What your dog hears is really loud and travels up to 1.5km. Adjustable through a wide range of frequencies using a screw piston mechanism enabling you to tune it to suit your own dog, this is the most versatile silent dog whistle that can be used with all breeds. A booklet is supplied with each one giving easy instructions on adjusting the whistle and training your dog. It is designed with special air directors to tightly control the frequency produced and generates over a mile of sound with minimal effort. Much of its original elegant shape from the period of Art Deco has been retained having been conceived by Clifford Hudson, son of founder, Joseph. Polished solid brass lasts for decades. This is the ultimate silent dog training whistle.

In every one of its 15 decades, so far, ACME has invented and patented a new and unique whistle that has continued to move the industry forward. From the first sports referee whistle in 1884 to the Hellova Safety whistle in 2014, ACME remains unequalled in any field you choose.