Aeotec Water Sensor, Z-Wave Flood & Leak Sensor

$49.99 (as of April 20, 2019, 4:14 pm) & FREE Shipping. Details $29.95

Monitor and protect against leaks and floods in real-time. Can also detect the absence of water when used with tanks
Super accurate; can detect as little as 0.03% of an inch of water
AAA battery-powered and wireless with 1 year battery life

Usually ships in 24 hours