A complete waste of time and money. The ones that are supposed to give off a high pitched signal are totally ignored by most dogs and would have to be used in close proximity to them anyway. The collars that spray a puff of air or citrus do work till the dogs get used to them, but obviously it would have to be the owners who put them on the dogs. The shock collars are cruel and barbaric (and now banned in Wales - but not the UK yet). The corrector sprays have to be used by experienced people to make sure they have the desired effect, and can be dangerous if used near to a dog that takes no notice of it - i.e. don't rely on one to stop a dog attacking, as they can make the dog even more aggressive.
Basically all they can do is to report it to the council. who will write to inform the owners that a complaint has been made, and that if it continues they could monitor the barking and if it was proven to cause a nuisance they could (eventually!) be taken to court if they did not stop it.
However, my neighbours have reported me several times and the monitoring equipment put in next door proved that my dogs do not bark excessively or for long periods - they bark when the postman comes, or uninvited callers such as Jehovas Witnesses and also when the neighbours bloody cats sit on my fence waiting to find a spot to crap in my garden.