The first sensor should go where the most expensive failure happens. Water damage from a burst washer hose, a failed water heater, or a leaking supply line commonly runs into the thousands of dollars. The sensor itself is $15 to $30. A 10-sensor set with whole-house notification costs under $200. The math is the same as for smoke alarms: cheap insurance against expensive failures that announce themselves loudly only after a lot of damage is done.
The eight priority locations
- Under the water heater. Catches drips from the tank, the T&P discharge tube, and the supply connections. Place inside the drain pan if there is one, against the back of the cabinet otherwise.
- Behind or under the washing machine. Catches burst hoses (the single highest-cost residential plumbing failure). Sensor goes on the floor near the back of the machine.
- Under the dishwasher. Catches door gasket failures, supply line drips, and drain line leaks. Most dishwashers have a few inches of clearance under them; slide the sensor in from the front.
- Behind the refrigerator (water line). Catches the ice maker supply line, which is plastic on many models and a known failure point. Sensor on the floor behind the fridge.
- Under every kitchen and bathroom sink. Catches supply line and trap leaks. One sensor per cabinet.
- Near the sump pump. Catches pump failures before the basement floods. Sensor near the pit, just above floor level.
- At every toilet base. Catches supply line failures and wax-ring leaks. Sensor on the floor next to the base, on the side most likely to get wet.
- In the laundry pan / drain pan if your washer or water heater is in one.
Second-tier locations (after the eight)
- Near the HVAC air handler condensate drain (especially if the handler is in an attic or above finished space).
- Basement floor near foundation walls if you have any history of seepage.
- Near the main water shutoff, where supply pipes can fail.
- In any crawl space where plumbing runs.
- Behind a tankless water heater.
- Near a water softener if you have one (brine tank overflows are common).
- Near a refrigerator with an in-door water dispenser.
- Under any window with a history of leaking during storms.
The right sensor on the floor
- Sensors detect water when conductive contacts touch a few millimeters of water.
- Place them on the floor (or in the drain pan), not on the wall or on top of the appliance. Water flows down.
- Place them at the lowest point of the area you're protecting. Floors are rarely perfectly level; water finds the low spot.
- If the area might get wet from condensation or splashes (under a kitchen sink, near a shower), use a sensor with adjustable sensitivity or position it slightly away from normal drip zones.
What kind of sensor
Three categories, in order of capability:
- Local-only audible alarm. $5 to $15. Battery-powered. Loud beep when wet. Useful only if someone is home to hear it.
- Wi-Fi smart sensors. $15 to $40 per sensor. Connect to a phone app and notify you remotely. Most popular brands: Aqara, Eve, SmartThings, Govee, Moen Flo. Some require a hub.
- Sensor + automatic shutoff. $400 to $1,500 installed. Includes sensors plus a powered valve on the main water line. When any sensor triggers, the valve closes the main automatically. Best protection, especially for vacation homes and homes with frequent travel.
For most homes, the Wi-Fi smart sensor tier is the right starting point. It catches leaks early and notifies you regardless of where you are. The automatic shutoff is worth considering for second homes, vacation homes, and any home you leave empty for weeks at a time.
Batteries and testing
- Most leak sensors use CR2032 or CR123A batteries. Lifespan 1 to 3 years depending on model and how often they communicate.
- Smart sensors report low battery to the app well before they fail.
- Test each sensor every 6 months by dipping the contacts in water briefly. Confirm the alert reaches your phone (Wi-Fi models).
- Replace batteries on a calendar rather than waiting for low warnings, especially for sensors you don't see often (behind the fridge, under a far cabinet).
What a leak sensor doesn't do
- Doesn't fix the leak. It tells you about it. You still have to act on the alert.
- Doesn't catch slow leaks that evaporate before the sensor sees standing water (rare but possible).
- Doesn't catch leaks in places you didn't put a sensor.
- Doesn't catch a roof leak that flows along framing for 20 feet before showing.
For roof leaks, attic moisture sensors are a separate category. For "leak that I'd never have seen otherwise" coverage, the standard 8 priority locations catch the highest-frequency failures.
For vacation homes and frequent travelers
Consider the automatic shutoff system. A leak sensor that notifies your phone is useful only if you can act on it. If you're traveling internationally with poor connectivity, or if the home is empty for weeks, an automatic shutoff that triggers immediately on any sensor is the better insurance.
Some insurance companies offer discounts (5 to 13% off premiums) for homes with whole-house leak detection and automatic shutoff. Ask your insurance agent before installing; they often have approved products.
Good maintenance rhythm
- One-time: place sensors at all 8 priority locations.
- Every 6 months: test each sensor by dipping briefly in water and confirming alert.
- Yearly: replace batteries on a calendar rather than waiting for low warnings.
- After any plumbing work: reposition sensors that may have moved.
- After any leak event: investigate, fix, and reposition the sensor for next time.
- Ongoing: confirm Wi-Fi sensors are still connecting to the app monthly. Sensors with stale notifications are the same as broken sensors.