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Where should you put water leak sensors in a house?

Updated August 2026

20–30 minutes · Easy DIY

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Cover the five spots that produce most household water damage first: the floor under the water heater, behind the washing machine, under the kitchen sink, under each bathroom vanity, and beside the sump pit. Add the dishwasher kick plate and the toilet supply stop next. The whole install runs 20 to 30 minutes, needs no tools beyond a phone, and costs $15–30 per sensor, which is a rounding error against the $5,000–15,000 a burst supply line does to flooring, drywall, and everything stored on that floor.

What you need

Before you start: Water and power do not mix, so keep sensors on the floor and never on top of an extension cord, a power strip, or a plugged-in transformer. If you come home to standing water, cut the circuit at the panel before you step into it, then close the main water valve. Learn where that valve is before you need it: a sensor buys you the 10 minutes to reach it, but it does not stop water by itself. And treat a wet sensor in a basement as a live alarm rather than a false positive until you have looked with your own eyes.

Steps

  1. Pair every sensor to the app on the kitchen counter before you place any of them. Naming them at the table beats crouching behind a washing machine trying to read a serial number.
  2. Set the first sensor flat on the floor under the water heater, at the low corner, and inside the drain pan if one is fitted. Tanks fail from the bottom, so this is the highest-value sensor in the house.
  3. Place the next two behind the washing machine and under the kitchen sink, contacts down, at the lowest point where water would actually pool rather than up on a shelf or riser.
  4. Work through the remaining risk points: each bathroom vanity, behind every toilet at the supply stop, at the dishwasher (slide the sensor under the kick plate), and next to the sump pit where it catches overflow before the floor takes it.
  5. Cover a finished basement and any second-floor laundry after that. Those leaks do their damage through a ceiling for hours before anybody notices a stain.
  6. Test each sensor by laying a damp paper towel across the contacts, and confirm the alert reaches your phone within 60 seconds. Fix a sensor that fails the test now, not in February.
  7. Route notifications to two people, with push and text both switched on. A sensor that only pings a muted phone at 2 a.m. is decoration.
  8. Photograph the main water shutoff and the water heater shutoff, then set a yearly reminder to test the sensors and swap the coin cells.

Or hire it out

A handyman or plumber charges $75–150 to place and test a full set of sensors, which earns its keep mainly when the water heater sits in a tight attic or crawlspace. The larger spend is the automatic shutoff valve that closes the main when a sensor trips: $400–800 for the device and $500–1,200 installed.

Done. Now the part everyone skips: doing it again on schedule. Log it in OnOtto and the next reminder for leak sensor setup sets itself.

Log this task, get the next reminder

Frequently asked questions

Do leak sensors work if the internet goes down?

The onboard siren still sounds, but no phone alert leaves the house. Wi-Fi sensors depend on your router and the vendor cloud, and hub-based Z-Wave or Zigbee sensors need the hub online to push anything. Pick models with a loud local siren, around 85 decibels, so they earn their keep offline, and put the hub and router on the same small battery backup if you travel often.

Which spots do people forget?

Four come up again and again: the second-floor laundry, the refrigerator ice-maker line, the water softener or whole-house filter cabinet, and the condensate pan under an attic air handler. All four sit above finished space, which makes them the expensive failures. If you have exactly one spare sensor, put it under whichever appliance sits above a ceiling you would hate to replace.

Is a sensor enough, or do I need an automatic shutoff valve?

A sensor tells you; a valve acts for you. With the house occupied most days, sensors plus a clearly labeled main shutoff handle the common case. If you travel, own a second home, or nobody is around during the workday, the automatic valve is the version that stops a flood at gallon 5 instead of gallon 500. Budget $500–1,200 installed and ask your insurer what discount applies.

How often should I test them and change the batteries?

Test once a year with a wet paper towel, and change the cells every 12 to 24 months or as soon as the app reports low battery. Most sensors run a CR2032 or a pair of AAAs, so a full house is $10–25 in batteries. Units under a water heater collect dust and corrode at the contacts faster, so wipe those two contacts whenever you test. The schedule is on how often to test water leak sensors.

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