The first ever silent dog whistle, invented by Acme in 1935. They say every dog will respond to this whistle with adjustable frequency to enable teaching of a variety of commands.
The modern, improved whistle is the perfect dog training tool for town or country, close or distance work. Adjustable frequency range can be tuned to your dog's hearing.
The whistle is effective up to two miles (3km) subject to weather conditions, and the abilities of the dog and the trainer.