Reflexdle is the classic reaction test played with everyone in the room at once. You wait while the panel is red and click the moment it turns green. Your average across three trials is your score, and the lowest average takes the round.
How it works
In each trial the panel turns red first and waits a random 1.5 to 4 seconds. Because that interval is random you cannot count it out; you have to wait. The gap between the switch to green and your click is measured in milliseconds.
Click early and the trial is not wasted, but you take a 500 ms penalty. Pre-emptive clicking on its own wrecks your average. After three trials the average is computed and submitted automatically.
Scoring
Lowest average reaction time wins: first +3, second +2, third +1. For reference, typical human visual reaction sits in the 200-300 ms band. An average below 180 ms is very good; around 150 ms you are either a professional player or you got lucky.
About reaction time
What you are measuring is not pure reflex but the sum of the signal reaching your eye, the brain processing it and the order travelling to the muscle. Reaction to a visual cue runs roughly 30-40 ms slower than to an audio cue, because sound takes a shorter path to the cortex. Age, fatigue and caffeine each move the number by tens of milliseconds, so your score first thing in the morning differs from your evening one. Losing a round does not mean your reflexes are poor, only that this is where you are right now.
Tips
Rest your finger on the button. A finger coming down from above costs 30-40 ms.
Look straight at the panel. Peripheral vision registers the colour change noticeably later than central vision.
Never click early. A 500 ms penalty spread over three trials is a 167 ms load on the average; no gain covers that.
Hold your breath. Breathing during the wait adds a small delay, a well-known athlete trick.
Hardware counts. A wireless mouse and a high-latency display add a few ms each; on desktop a wired mouse has the edge.