The Basement Watchdog Compact 110 dB Water Alarm w/360° Sensing Technology (BW-WA360)

Outdoors, a slow leak waters the lawn. In a basement it spreads under shelves and along walls until somebody notices. This alarm is a small battery-powered box, 2⅜ × 1 × 3¼ in (6 × 2.5 × 8.3 cm), that sounds at 110 dB when it touches water. The listing says it senses as little as 1/32 in (0.8 mm) and detects water on any of its sides.

It is deliberately simple: one 9 V battery, no app, no wiring. That also means it only helps when someone is in the house to hear it. Before a trip, look over the hose joints and consider draining the tub.

Tip: Pour a cup of water on the floor near the tub once and watch where it runs – that low spot, close to the hose joints, is where the alarm belongs.