[…], such gadgets are built around vibrating motors originally designed to run industrial sieves. They come with multiple modes: vibration only, pounding only, or a combination of the two. A fourth option activates both, along with other random sounds including static, persistent knocks, and even piercing shrieks.
The floor-shaker serves one purpose: when installed on the user’s ceiling, the deafening noise it makes is projected into the house above