Reaction: Press and Hold
A reaction-time tester with one twist: it measures the moment you lift your finger, not the tap. By having you hold first and release on the signal, it strips out the finger travel that taps sneak into the number, so what you get is closer to your true reaction time.
Most reaction testers measure "see the signal, then tap." That mixes two different things: how fast you perceive the signal, and how long your finger takes to travel down and hit the glass. The travel is motor noise that has little to do with reaction time.
Reaction removes it. You rest your finger on the screen before the trial starts, so there is zero travel distance. The clock stops the instant you lift off. Lifting is a simpler, more consistent action than a full press, so the measurement isolates the perceptual side more cleanly. Everything runs on device, with no accounts, no ads, and no tracking.
You put your finger down before the trial starts. Finger already in contact, zero travel to add noise later.
After a random delay the screen flips to the go state. Lifting early is a false start and simply resets, so you cannot game it.
The instant your finger leaves the glass, the clock stops. That release time, in milliseconds, is your result.
After the round you get the average, best, worst, and consistency, plus a trend over time and your own distribution.
A small idea taken all the way to the App Store: the measurement method, the interface, the stats, and the polish, designed and coded end to end. No accounts, no ads, no tracking, and every result stays on your device.