Ears are faster than eyes
In laboratory conditions, people react to sound roughly 30–50 ms faster than to light: auditory signals take a shorter path through the brain than visual ones, which have to be processed through the retina and visual cortex first. Sprinters live on this — it is why races start with a gun, and why a start is called false below a certain reaction threshold.
On a web test the gap partly closes, because audio output has its own latency — Bluetooth headphones can add 100–200 ms before the beep ever reaches you. Wired headphones or speakers give the most honest numbers. Whatever you use, keep it consistent between runs so your history stays comparable.
How this test works
The shape is identical to the visual reaction test: a random 2–5 second delay, then the signal — except the signal is an 880 Hz beep and the panel deliberately shows nothing when it fires. Clicking before the beep is a false start and the attempt is discarded.
Take both tests and compare your medians. Most people find their audio and visual scores within a few tens of milliseconds of each other; a large gap usually points at hardware latency rather than your nervous system.