Reddit mentions of KCSC Mini Bark Control Deterrent, Anti Barking Device, Dog Training Tool, Stop Barking, Safe for All Dogs, Indoor & Outdoor use, up to 50 Feet Range (Upgraded)

Unfortunately, I do not have any specific product recommendations. I'd say in general look at amazon reviews. The highest rated ones are:

Modus Anti Barking Device, Ultrasonic Dog Bark Deterrent and 2 in 1 Dog Training Aid Control Range of 16.4 Ft (4xAAA, Handheld, On-Demand Button Press)

KCSC Mini Bark Control Deterrent, Anti Barking Device, Dog Training Tool, Stop Barking, Safe for All Dogs, Indoor & Outdoor use, up to 50 Feet Range (Upgraded) (1x9V, Passive, runs all the time when switched on)


However the page from the first model says:

>The conditioned reflex of the dog usually takes 3-10 days to form, adapt and consolidate. During this period, the owner should continue to train the dog patiently. If you can't achieve the results you expect, we are very sorry, we will do our best to improve the performance of the products.

>
>Note:

1. The product may not be effective on dogs with hearing problems.
   
2. The product cannot be used for dogs under six months.
   
3. This device is not intended to provide protection against aggressive dogs.
   
4. Different dog breeds may react to the ultrasonic sound differently. [ People who train their dog to "come" when they make the noise might actually be attracted... ]
   
5. For optimal results, please use the product as a training aid, along with other tools/commands. Be patient during this training process.
   
   They are typically sold for training your own dog so the documentation and pages tend to focus on using it to get a dog to do whatever it is you want. How they work on neighbors dogs or dogs in the general public (single encounter) to stop barking/approaching might be different. The comments might give an idea how well it works for those those off-label uses.
   
   The basic idea is that when the dog starts barking, fire the device as quickly as possible and stop it as soon as the dog starts. The idea is that the animal hopefully puts together barking and an unpleasant noise, and that the unpleasant noise stops when they do. This makes me think the on-demand button press will work better, but people might see you carrying it.
   
   If you leave it on all the time, to make a "bubble" around you, it might cause dogs that were not barking to start barking. Ultrasonic sound is also highly susceptible to walls and obstructions. More or less assume it is "line-of-sight." Low-frequency sound like bass travels better though physical obstructions. Non-handheld ones putting it in a purse or backpack might decrease its efficacy.