How Online Reaction Time Tests Work
A reaction test looks simple. Something appears, you tap it, a number comes up. That number, though, is the total of a whole chain of delays, and only some of them happen inside your head. Once you see the chain, it's obvious why your phone and your laptop give different scores, and why some "scores" are physically impossible.
What the number actually measures
It starts with the screen. Before you can see the target, your display has to draw it. A 60 Hz screen refreshes every 16.7 ms and a 144 Hz one every 6.9 ms, so the target can sit waiting for the next refresh before it shows up at all. Many TVs add their own image processing on top unless game mode is switched on.
Then comes the part people mean by "reflexes". Light hits your retina, your visual system recognises the target, your brain decides to move, and the signal travels down to your hand. This is the bit you can train, and the bit that changes when you're tired.
Finally your device has to notice the tap. A standard USB mouse reports to the computer 125 times a second, which can mean up to 8 ms of waiting, while gaming mice report 1,000 times a second. Touchscreens scan for touches on their own schedule, which is part of why phones tend to score a little slower.
Add the screen and the input device together and the hardware share can be anything from about 10 to 20 ms on a fast gaming setup to well over 50 ms on some phones and TVs. That's why comparing scores across devices is never entirely fair, and why your best result will probably come from your quickest one.
How this test times you
Browsers can measure time very precisely, as long as the test is built with care. This one starts the clock using the timestamp of the exact animation frame the target first appears in, rather than the moment the code asked for it to be shown. It stops the clock using the timestamp your device attached to the tap itself, so if the page happens to be busy for a split second, that hiccup isn't added to your time.
It also reacts the instant your finger touches down. Many web games wait for a full "click", which only fires once you lift your finger again, quietly adding the length of the tap to every result.
Only a tap or click that lands on the target counts. Pressing a key doesn't, because the keyboard would let you skip the aiming that everyone else has to do, and that wouldn't be fair on the leaderboard.
Why the wait is random
If targets appeared at a steady beat, you could tap along to the beat instead of reacting to what you see, and your score would measure timing rather than reflexes. Each target here appears after a random delay picked by the server, so the only way to be quick is to genuinely react.
Why anything under 100 ms is a false start
There's a floor to how fast a human can respond to a signal, because the eye, brain and muscles all need time to do their jobs. Athletics draws the line in the same place. Under World Athletics rules, a sprinter whose blocks detect a reaction faster than 0.100 seconds after the gun is charged with a false start, on the basis that nobody can genuinely react that quickly. This test uses the same 100 ms limit, and anything faster just restarts the round. There's more about reactions in athletics, baseball and tennis in reaction time in sport.
Why five rounds, not one
A single reaction is noisy. A blink, a moment of distraction or a lucky guess can move it by 50 ms or more. Averaging five rounds gives a much fairer picture of your real speed, and the average is what the leaderboard ranks. Tap too early or too late and that round is replayed rather than spoiling the whole game.
How the leaderboard stays honest
A browser game runs on the player's own device, so anyone determined could try to send a fake score. Every score is therefore checked on the server before it counts. It must come from a game the server started, every round has to respect the 100 ms human limit, and the whole game can't have finished sooner than its random delays would physically allow. Timings that look too machine-perfect are rejected as well. The about page has the details.
Getting an accurate score
If you can, play on a computer with a wired mouse and a high refresh rate monitor. On a TV, switch on game mode. On a laptop, plug the charger in, since battery-saving modes can hold performance back. Close any heavy tabs and apps, play one warm-up game, and then go for it. For everything that isn't hardware, see what affects reaction time.
Sources
- World Athletics, Competition and Technical Rules: false start rule (reaction time under 0.100 s).