ATL LLC Dog Bark Control Anti Barking Device Ultrasonic Dog Bark Deterrent Training Tool, Outdoor & Indoor Uses, Safe for Dogs, Pets and Human, Birdhouse Shape up to 50 Feet Range

Works pretty well. Sometimes it will make a noise on its own though and doesn’t always go off when dog barks. May just need new batteries

Have four chihuahuas and when one starts barking the others join in. Only have on low and it is working on two of them. The other two will bark....but I believe not as long. Only have used for a short time, so we shall see.