Optical + Accelerometer
When I met with Logitech while setting up for our Hardware Workshop at Quakecon this year, they wanted to show me a new mouse they were coming out with. Of course I was interested, but to be honest, mice have seemingly gone to a point where I could very rarely tell them apart in terms of performance. Logitech promised me this would be different. The catch? The G402 Hyperion Fury includes not just an optical sensor but an accelerometer and gyro combo.
Pretty much all mice today use optical sensors to generate data. The sensors are, basically, taking hundreds or thousands of photos of the surface of your desk or mouse and compare them to each other to measure how far and how fast you have moved your mouse. Your PC then takes that data from the mouse at a USB polling rate, up to 1000 Hz with this mouse, and translates it into mouse movement on your desktop and in games.
There is an issue though - at very high speeds of mouse movement, the optical sensor can fail. It essentially loses track of where it is on the surface and can no longer provide accurate data back to the system. At this point, depending on the design of the mouse and driver, the mouse may just stop sending data all together or just attempt to "guess" for a short period of time. Clearly that's not ideal and means that gamers (or any user for that matter) is getting inaccurate measurements. Boo.
To be quite honest though, that doesn't happen with modern mice at your standard speeds, or even standard "fast" gaming motions. According to Logitech, the optical sensor will start to lose tracking somewhere in the 150-180 IPS, or inches per second. That's quite a lot. More precisely that is 3.8 meters per second or 8.5 miles per hour.