not silent but effective: I remember up to 3 km and easily my dog German shepherd-of-5 years old when he took the crazy idea to go for a walk without me. For quick and effective learning, You simply whistling every time you give him his meal, a treat, a hug, a start and your dog will associate pleasure whistle-like "nice, let's ride!"; made the walk back to the regular whistling. that's it! This ultrasonic whistle is very stylish and small enough to be hung on the key ring or the dog's leash. Do not rust. I recommend
