In South Korea, people who can’t convince their neighbors to keep the noise down are increasingly turning to expensive but effective sound systems designed specifically to irritate neighbors.

South Korean media first started reporting on these specialized sound systems back in 2016, when they were viewed as an almost funny way that some apartment building neighbors used to settle their disputes regarding noise. However, as time went by, they became incredibly popular as they delivered on the promise of making next-door or above-floor neighbors pay for ignoring requests to keep noise levels down. There are now different types of wall-mounted speakers designed specifically to annoy.

Online commerce and auction sites in South Korea feature various types of specializes “revenge sound speakers”, with varying designs, power output, connectivity options and functions. All have one thing in common though, they are meant to be mounted on the wall shared with the offending neighbor, with the diaphragm pointing at the wall.

Although there are literally dozens of different revenge speakers to choose from, there is one that South Koreans seem to love the most, at least according to the number of online reviews and overall rating. The Smartor speaker is an oval-shaped device that reportedly torments your neighbors while allowing you to go on with your day undisturbed. At around 170,000 won ($150), it’s not the cheapest speaker money can buy, but people say it’s more than worth the money.

“The output comes out very well. The effect is great,” one satisfied customer wrote.

“I feel at ease, because I can have my revenge on the apartment above me,” someone else commented.

Sound systems designed specifically to annoy neighbors are not illegal, but authorities recommend other ways of dealing with noisy neighbors, such as civilized dialog, or using official channels to report inappropriate levels of noise during certain hours. However, the growing popularity of these devices suggests people love them.

Experts warn that specialized noisemakers may seem like the perfect way to get back at noisy neighbors, but in most cases it only escalates conflict, often leading to situations that can only be resolved by one of the parties moving from the building.

Interestingly, in China, people rely on “building shakers” to get back at noisy neighbors, which is reportedly even worse than the annoying noisemakers used in South Korea.