Each button blinks on its own clock, and no two clocks are exactly alike. Light up three warnings together, and a minute later they flash like car indicators in a traffic jam, each to its own beat. On a panel that looks broken.
Syncing them one by one wouldn't work; the first would drift before the last got the message. I²C has an answer almost nobody uses: the General Call, address zero, which every device can listen to at once. The rule in the firmware is simple: when a General Call arrives, restart your blink. The message carries no data at all.
The controller sends one every few seconds, too often for any drift to show, and the whole panel snaps back into step at the same instant.