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Most modern laptops have some sort of volume control buttons. Usually these are a set of Fn keys on the keyboard, but convertible laptops with screens that can flip around for use in tablet mode often have volume buttons on the side.
But adjusting audio volume with buttons can be a finnicky experience that requires multiple clicks to dial things in. The SoundSlide is a laptop accessory that takes away the need to click. It's a capacitive touch controller that plugs into a USB Type-C port and lets you control the volume on any Windows, Mac, or Linux laptop by sliding your finger across the surface.
Measuring just 20.9 x 6.9 x 3.5mm, the device sticks out a little from a USB-C port, but overall it's designed to look like it's almost part of a laptop since it takes up very little space.
As CNX Software notes though, what it does take up is a USB-C port. If you have a laptop with two or more such ports, that might not be a problem. But if you've only got one it'd be an interesting choice to sacrifice it for a slider that's only designed to do one thing.
That said, it has the potential to be a helpful (and customizable) little addition to a PC. SoundSlide offers a firmware configuration tool that lets you adjust settings like touch sensitivity, scale, and orientation. And the company behind the device has open sourced "the core elements that power SoundSlide" by releasing schematics, firmware source code, and a command line configuration tool.
Perhaps that could open the door to support for third-party applications.