First to tell you about how these devices work let’s tell you about dogs themselves. A dogs nose is structured differently then a humans and gives it a sense of smell that is thousands of times better then a humans. How is it different ? A dogs nose has about two hundred million of olfactory receptors. A olfactory receptor allows you to sense and identify even the more minute odor molecules. A dog has 25 times more then a human. So with this it should be obvious that a dog has a smell that is far far more sensitive then a humans. Now what does this mean about this device I bet you wonder. Well the citronella spray that is used in these anti-barking collars are designed to be unpleasant to these super sensitive noses. They don’t harm or irritate the nose it’s just a foul smell. This will quickly show your dog that barking is not the right thing to do and will result in a nasty smell. How quickly do these devices work ? They can be extremely fast or they can take a few weeks but usually you will notice a difference fairly quickly.
Sunbeam Sonic Egg Bark Control Device for Dogs Review - The Spruce
As anti barking devices, dog collars are in most cases fitted with shock chips. These chips are controlled through remote and give shock at any time the dog intends to bark.
Do ultrasound devices, a dog anti-barking device in particular
These are used with some remote controlled or set up sound devices which transmit the sound of the dog and turns it into a scary sound which is not pleasant to the dog. In this vain, the dog will stop barking immediately the sound reaches it.
Pros & Cons of Barking Devices for Dogs | Dog Care - The Daily Puppy