Reaction Duel — 2 Player
A split-screen reflex duel for two players on one phone or keyboard: wait for green, tap first, first to 5 rounds wins.
Two players, one device. Each player owns one half of the screen — or the A and L keys on a keyboard.
Wait for green, then tap your side first. Tapping early loses the round. First to 5 rounds wins.
How it works
- Press Start duel, then each player rests a finger near their half of the screen (or over the A and L keys on a keyboard).
- Watch the screen: it shows Wait, then turns green after a random 1.5–5 second delay — tapping before green loses the round instantly.
- The first correct tap after green wins the round and shows the reaction time in milliseconds; first player to 5 rounds wins the match.
Frequently asked questions
- How does Reaction Duel decide who wins a round?
- Both players wait for the screen to turn green after a random delay. The first player to tap their half (or press their key) after green wins the round. If a player taps while the screen still says Wait, that counts as a false start and the round goes to the opponent.
- How accurate are the reaction times shown?
- Times are measured with the browser’s high-resolution performance clock from the moment the green signal is drawn to the moment your tap or keypress is registered. Touchscreen and browser input latency adds roughly 10–40 ms that the game cannot remove, so treat times as consistent within a match rather than lab-grade measurements.
- Is the delay before the green signal predictable?
- No. The wait is drawn from the browser’s cryptographic random number generator and lands anywhere between 1.5 and 5 seconds, so there is no rhythm to memorize. Anticipating the flash is risky by design — an early tap immediately loses the round.
- Can two people really play on one phone?
- Yes, that is the intended setup. The screen splits into two large touch zones, left versus right, and both portrait and landscape orientations work. On a desktop or laptop, player one uses the A key and player two uses the L key instead of tapping.
- Does the game send any data to a server?
- No. The entire game runs in your browser with no network requests, no accounts, and no tracking of results. Scores and reaction times exist only on your screen and are gone when you leave or refresh the page.
About this tool
Reaction Duel is a free two-player reflex game you play on a single device. The screen splits into two big touch zones — left player versus right player — and both of you wait for the same signal. After a random delay the screen flashes green, and the first correct tap takes the round. Tap too early, while the screen still says Wait, and you hand the round to your opponent. The first player to win 5 rounds wins the match, with a large running score and each winning reaction time shown in milliseconds.
Everything runs client-side in your browser. The pre-signal delay is generated with the Web Crypto API, so it is genuinely unpredictable between 1.5 and 5 seconds — there is no pattern to learn and no way to game the timer. Reaction times are measured with the high-resolution performance clock, from the frame the green signal appears to the instant your tap or keypress lands. No data is uploaded anywhere; the page makes no network requests while you play.
It works well as a quick settle-the-argument game: who buys coffee, who picks the movie, who goes first in a board game. Teachers use simple duels like this to demonstrate human reaction time, which typically lands between 200 and 300 ms for a visual stimulus, and the per-round millisecond readout makes that concrete. Because false starts lose the round, the game also punishes guessing, which keeps matches honest.
A few practical tips: hold the phone flat between you so neither player has an angle advantage, and rest a fingertip lightly above your zone rather than hovering high. On a keyboard, player one takes the A key and player two takes the L key, which keeps hands far apart. Landscape orientation gives each player a wider zone, but portrait works fine — the touch areas stay large either way.