A urinous wet alarm to detect a soaked diaper and generate an audio alarm to alert replacement includes a shell to house a test IC. The test IC connects to a lithium battery, a thin alarm speaker and one end of a sensing unit which is a pliable, elongate, narrow and thin plate and has a detection circuit consisting of two conductive wires of opposite polarity extended from the shell. The sensing unit may be inserted into a test insertion hole formed on a diaper during production. Urine soaked the fluid absorption layer of the diaper makes the conductive wires conductive, and the test IC determines the urine overflow condition to activate the thin alarm speaker to generate an audio alarm.