According to the product description, the max range is 30 ft. I'm going to assume the sound is audible to any dog within range. There are three settings-- just flash light, medium sound, and max sound. I have been using the middle "training" setting. When I hit the button the light flashes as well. This is actually good because I can see how long the device is activated and I am literally hitting it for one second!
Neither Fil nor Koko has shown any adverse reaction to it when I used it on Benson and they were in the room. No crying whining hiding--nothing. They just shut up. Koko also barks at dinner time and after I told Benson Quiet! Koko never made a peep!
Following up on second use on Benson:
He goes crazy barking when I leave the house. The others don't and never did. So I took it with me to the garage door, and he started gearing up for his "Mama's leaving" hissy fit. I said Quiet!, he let out one yip, I hit the button and said Quiet again. He trotted off down the hallway quietly. I went into the garage, left the device on the workbench so I could grab it for the "Mama's home" hissy fit training session. According to my husband, Benson started barking again after I was in the car (I'm betting the garage door going down triggered it) and he couldn't hear the tv. He looked over here at my desk but no device! So he grabbed the Firestick remote, got up and showed it to Benson and he shut right up. LOL.
I grabbed the device when I came back in. I had three calm dogs standing at the garage door. Yes, Benny saw it in my hand

For the first time since Benson bonded to me, I came home and he waited with the rest of the family until I put my purse and packages down, then got on the floor to give all three hugs and kisses!