Zone Watch
One sentry in every row, column and coloured region — and none of them touching.
One sentry in every row and every column.
Tap a square once to rule it out, again to post a sentry, once more to clear it. Every row holds exactly one sentry when you are done, and so does every column.
Tap a square once to rule it out, again to post a sentry, once more to clear it. Every row holds exactly one sentry when you are done, and so does every column.
The heavier lines divide the board into coloured regions, one for each row. Every region holds exactly one sentry too — the constraint that makes the board solvable, and the one a row-and-column check alone will never give you.
Sentries cannot sit side by side, one above the other, or corner to corner. Place two that touch and both turn red until one of them moves.
Tap cycles · keyboard: arrows move, space cycles, backspace clears
Got it — play