The video below will play high sounds (similar to a dog whistle) that humans can barely or not even hear at all. Interesting here at the house testing what both the puppy and I can hear, and later, only what the puppy can hear. The expression on Saucy's face and him looking around tells me he can hear it. Kinda funny! Enjoy!
I bet it has a lot to do with the speakers that are producing the sound. I'm on an iPad. Dog one awake but not alert right next to me didn't react till sound 5, and then also to 6 and 7, the same sounds I could hear. Dogs 2 and 3 and 4 were passed out from chasing Easter bunnies all morning reacted to none. Dog 5 was hard to gauge, a little spazzy, but did try to attack the ipad on sound 5 and then ran away on sound 6.