In this context, I'm referring to gadgets which give a dog a negative consequence of an action ie something which inflicts discomfort, pain or restricted movement when a dog does something "wrong". In short, they don't work. That is to say, they don't fix the underlying problem or the root cause of the behaviour in the long term. At best, they cover up the problem and give the owner a false sense of security that the problem is cured. At worst, the gadget replaces one problem with another - a fear of the item or the situation, making it worse for a dog that's already confused by trying to deal with things he doesn't understand in the human world.
There are a number of different varieties on the market of slightly different designs. The idea is that the headcollar allows the dog's handler to control the dog's head and also that the headcollar tightens around the dog's head or face when they pull, so deterring them from pulling because it's uncomfortable. The dreaded choke chain is used for the same principle. However, under that headcollar, the dog still wants to pull, still feels the need to pull and wants to resist anything that's stopping him doing the job of leading the walk. Take the headcollar off and you're back to square one. Worse still, the dog gets used to the straps digging into his face and accepts that they just have to put up with it in order to do their job no matter what. Instead, what the dog needs is evidence of calm leadership from the person at the other end of the lead. This takes a little time and practise but is so worthwhile when the end result is years of stress-free, gadget-free walks. See the Walking the Dog (Part 1) and Walking the Dog (Part 2) articles for more detail.
For some dogs, the shoulder harness is a safe and comfortable alternative to a standard collar - for example, very small dogs or dogs with neck problems. However, as a cure for pulling, just like the head collar, it disguises the underlying problem and tricks the handler into thinking they've achieved a quick fix. When you think about it, how do huskies pull a sled? A shoulder harness makes it easier for them to pull!
These are usually in the form of collars which, when activated by the sound of a bark, emit a spray into the dog's face or emit a high frequency sound which is painful on a dog's delicate ears. As described in the article Why Do Dogs Bark?, barking is a completely normal and natural reaction for a dog in certain situations. Problems occur when the barking gets out of control and just doesn't stop. There is an effective way to control barking which means a dog will still bark when necessary but can be stopped when no longer required. Once again, instead of looking for a quick fix and breathing a sigh of relief that the problem is sorted, owners would be far better off spending a little time and effort looking at the situations in which the barking occurs and dealing with them. Is it due to separation anxiety, or the dog feeling the need to guard the property when left in the garden alone for long periods of time, supposedly to entertain themselves? In these situations, the dog's stress needs to be reduced, not increased by adding a confusing "punishment" into the mix when he's doing what he believes is his job. If the dog is barking for attention, look at how you may be adding to that by feeding into it. Again, there is more detail in the Why Do Dogs Bark? article.
These are meant to stop a dog from doing something, when caught in the act, by startling him and scaring him into not doing it again. They can be manufactured products such as an aerosol which squirts air, or home-made such as stone-filled plastic bottles (used as a rattle) or a water spray. There are 2 disadvantages to these types of gadget. Firstly, the dog can just get used to it and realise he can simply ignore it. Or he can become fearful of an entire situation (eg going into the garden or going out for walks) or the person operating the gadget. Once again, there is no shortcut and no substitute for getting to the root of the problem and fixing it long term. So look at the cause of the dog's bad behaviour and how it can be prevented or cut short in a calm, non-confrontational way without inflicting fear.
In my opinion, the worst gadgets of all. A remotely operated collar gives the dog an electric shock when a button is pressed by the operator (or in the case of the fence, when the dog passes a certain point). The use of these collars is banned in Wales but sadly not in the rest of the UK. Supporters will say that the electric shock is only mild but I bet they wouldn't use it on a person! For canine victims, the only outcome is trauma - fear and terror of what they were reacting to in the first place and also fear of the person operating the collar. At some stage, that will turn into aggression when that person goes to place the collar on the dog (the same applies to the spray and ultrasound collars). At the risk of repeating myself, there is no substitute for spending time and effort getting to the root cause of the problem and working on a long-term solution - with professional help if necessary, but of course with a trainer/behaviourist who doesn't rely on gadgets.
It is often desperation that leads dog owners to turn to gadgets, especially when suggested or recommended by a trainer, pet shop, TV programme or magazine article. But there's always another way - as long as you are willing to put in some time and effort with your dog to help him for the long-term. He deserves that doesn't he?