Yikes this got long; TL/DR version: I personally believe it’s ok, as long as it’s used to modify the animal’s behavior and could actually be beneficial to the animal.
Having grown up on a farm, I’ve discovered that what is innocuous to me is considered harmful by others, so my opinion might not stand for the majority (but I’ll hazard it might for most of the rural folk). :-)
There are a few things to consider when examining the morality/ethicality of such a device. The primary question is: what is the user’s intent? If it’s for the thrill of watching the animal squirm, then there’s a problem, but if it’s to be used to modify the animal’s behavior, then, as long as it doesn’t cross certain boundaries, I don’t have a problem with it. Such boundaries would be things like causing excessive or permanent pain. A short amount of pain, quickly delivered and quickly removed, can effectively be used to modify behavior.
Personal anecdote: As I said, I grew up on a farm. (Full disclosure: My parents were not farmers, but all of my mother's relatives are, and my mother was until she married a park ranger, who had views very similar to the farmer relatives. I grew up in the middle of their combined land and helped out frequently, but got to avoid [most of] the 3 AM “find the cow before she dies trying to give birth” wake-ups.) ANYways, almost all of the relatives had cattle at one time or another. Cattle are notorious for finding ways to get out of pastures. And they’re persistent devils too. If they figure out that a particular section of fence is weak, they’ll keep trying and keep trying it until it gives and they get out. Do a bad repair job and a week later you’re going to be chasing a dozen cows across 3 miles of fields again. In addition, cows seem to have particularly itchy hides, and what’s the best thing available to scratch with? You guessed it, the barbed wire fence. Itchy hides that are apparently thick enough to shrug off multiple sharp pieces of metal. The fix? Electrify the fence. Now if Bessie noses the fence or rubs up against it, she’s going to have quite the shocking experience. But it ends as soon as she backs up, and there’s no lasting effect other than the cow going “Moo!” [Translation: “WTH?! That hurt!”] (Well … except for that one cow, but she was standing in water and was sick to begin with, poor thing.) Enough times and she’ll [hopefully] learn to not engage the fence. So, short term pain: a zap of electricity, for a long term gain: cows don’t get out, time’s not lost hunting them down, and innocent people are not at risk of going around a curve and suddenly having a thousand pounds of extremely fresh beef in the front seat with them. In other words, the cows receive a short, painful jolt of electricity in order to prevent them from risking being put down due to a broken leg or two. (That’s another side effect of growing up in the country, “Fido’s sick and it’s going to cost HOW much to treat him? Uh, how much to have him euthanized?”)
How does this huge ramble of an anecdote apply? Some areas have strict rules concerning animal noises, especially neighborhoods with Home Owner Associations. A lot of them have rules about animal noises and the owners of an incessantly barking dog could suddenly find themselves with a notice stating that their dog either shuts up or moves out. Getting rid of the dog runs the significant risk of it being taken to a pound where the chances are good that the animal will be euthanized. Not to mention the heartbreak some kid has when her dog gets taken away.
Ok, good intention check, does it still make it moral/ethical: maybe, maybe not. Do it wrong and it’s as bad as intentionally mistreating the animal. Have the setting too high and the animal could be injured is one way to do it; but I’m thinking more along the lines of being inconsistent. Few things drive me as batty as watching people haphazardly applying discipline, be it with their pets or their children. Mixed signals only causes stress and problems for all parties involved. So, if somebody wants to do this, they need to keep to a regime and not just blast the neighbor’s dog when there’s company over.
There’s also the risk of the neighbor figuring out what’s going on and having a fit about it. That’s getting into an area I’m not comfortable stating an opinion on without more consideration. I will say that it could easily go bad for the PSB user if the owner claims that they’re tormenting the animal, especially if it’s behind a fence and is not a direct physical threat to the person.
Then there's the whole angle of: is it any different than bark collars and invisible fences that use shocks to control the animal? Off the cuff I'd say yes. A bark collar or invisible fence is the owner applying discomfort to their animal, e.g. internal use whereas a PSB is a non-owner applying a similar method to somebody else's animal, e.g. external use. (And yes, I know that properly set it's not pain but a variable degree of discomfort, but that goes back to the preceding paragraph and how the owner might interpret discomfort vs. pain.)
Steve
The “Portable Dog Killer” potentially has less ethical uses. Back in 1988, an ultrasonic gun - disguised as a pair of binoculars - was used to try to prevent a horse winning a race at Ascot racecourse outside London, UK.
See http://articles.latimes.com/1989-11-01/sports/sp-229_1_ultrasonic-gun
Steve