Sentons has started marketing technology that aims to do away with gadget buttons and said it is working with two smartphone makers in addition to an existing contract with Asus.

Headed by Jess Lee, an engineer who sold his previous company to Apple, Sentons announced a sensor system that uses ultrasonic sound waves to detect touches, presses, and swipes on a variety of materials such as the metal edges around a smartphone.

The technology is already being used by Taiwan’s Asus and its partner Tencent in a phone designed for gamers that was released in China this summer.

In the Asus phone, the sensors allow gamers to hold the phone horizontally and tap “Air Triggers” along its top edge as virtual buttons with their index fingers while their thumbs tap the screen.

“Touch screens are great, but (phone makers) hadn’t been able to figure out how to add interactivity to the sides”, Lee told Reuters in an interview.

“With the thinner and thinner form factors, perhaps even all glass or with funky metallic edges that are really, really thin, there’s no space for buttons.”

The core of Sentons’ technology is a custom chip that sends out sound waves and contains a processor and algorithms for understanding various gestures.

Sentons is also working on a virtual jog wheel which allows users to scroll through apps on phones that have become too large to hold with one hand. Another project is a virtual shutter button to focus a phone’s camera, similar to the way a physical shutter button works on dedicated digital cameras, Lee said.

Beyond smartphones, Lee said the company hopes to add touch interactions to devices where screen space is either extremely limited, such as the frames of smart glasses or the bands of smartwatches, or where there are no screens at all, like the steering wheels of cars.