SayoDevice O3C mini: A Hall effect keypad for rhythm games like osu! and Geometry Dash

Hall-effect magnetic switches have become the gold standard for competitive rhythm and FPS gaming, and we’ve seen premium keyboards such as the Keychron Q16 HE 8K and even all-screen designs like the Centerpiece Pro released in the market. However, those devices come with a hefty price tag. Compared to those, the SayoDevice O3C mini is designed for a similar level of performance and ultra-fast responsiveness at a fraction of the cost.

The keypads are available in Outemu Pink, Gateron KS-20 White, or Gateron Jade Pro Green variants, and as these switches use magnetic sensors rather than physical metallic contacts, they can be triggered rapidly. This allows the switch to reset dynamically the moment it travels upward, rather than waiting to pass a fixed reset point, which is crucial for the rapid, repeated keystrokes in high-level rhythm games. On top of that, users can customize the trigger stroke to as low as 0.05 mm.

While searching for more information, I found multiple AliExpress listings and Reddit threads about the products, and the feedback is a mixed bag, where some feedbacks are positive with the device's input latency and overall response time. Some users argue that the underlying hardware scan rate needs to match the 8000 Hz polling rate to achieve absolute theoretical optimization.

The keypad also features a 0.96-inch IPS color display, which shows real-time telemetry data, including visible key travel distance and a keystroke counter. The display can also be customized with a custom text string, user IDs, or custom images via a web-based configuration tool. There's also a programmable aluminum rotary knob alongside the display, which can be mapped to functions like volume control or can be used to scroll through song lists.

The keypad features an ABS plastic chassis, hot-swappable switch sockets (supporting any magnetic pole/axis with a simple one-click calibration), and customizable multi-color RGB backlighting. Its available on AliExpress with a discounted price of roughly $29.13 (down from an MSRP of $68.37).