A slab leak is one of those home repair nightmares you really don’t want to deal with — water leaking from pipes buried in or under your concrete foundation. Repair costs can run anywhere from $500 to $4,000+ depending on how deep the line is and whether you need to jackhammer through the slab. The faster you catch it, the better.
This guide covers the tools and apps homeowners are using in 2021 to help detect or confirm a slab leak before calling a plumber.
Step 1: Do the Meter Test First
Before you touch any app, walk out to your water meter. Turn off every fixture and appliance in the house — including the ice maker, the irrigation timer, and the whole-house humidifier if you have one. Then look at the low-flow indicator on the meter (usually a small red or blue triangle). If it’s spinning and nothing is running, you’ve got a leak somewhere in the pressurized supply line. This doesn’t confirm a slab leak, but it narrows the field.
Apps That Can Help
Flo by Moen (Smart Water Monitor)
If you already have a Flo by Moen device installed on your main supply line, the companion app (available for iPhone and Android) will flag unusual flow patterns overnight. The app uses a “Health Test” mode — runs a brief pressure test on your lines and grades them pass/fail. As of the 2021 version of the app running on Android 9 or later, the test takes about 15 minutes and logs results automatically. It won’t tell you the location of the leak, but it confirms whether a pressurized line is losing pressure.
Phyn Plus App
Phyn is a Belkin-backed smart water monitor that pairs with a device on your main line. The app — tested here on an iPhone X running iOS 14 — learns your household water “fingerprint” over the first two weeks and then flags anything that doesn’t match. It’s especially good at catching slow, steady losses that a slab leak often produces. The downside: the Phyn Plus hardware ran about $699 at Home Depot in 2021, so it’s a bigger upfront investment.
LeakSmart App
LeakSmart works differently — it’s a sensor-based system where you drop small puck sensors near appliances and under sinks. The main app pairs over Z-Wave protocol, which means you need a compatible hub (SmartThings was the most popular hub ecosystem in 2021). Sensors retail for around $35 each. This won’t detect a slab leak directly, but if you’ve placed a sensor near a floor drain or in the utility area and it keeps getting damp, that’s a clue worth investigating.
Handheld Tools Plumbers Use (That You Can Rent)
Acoustic Leak Detectors
A professional acoustic leak detector listens for the hiss or rushing sound that a pressurized leak makes through concrete. Brands like Ridgid and Leica make these — plumbers use the Ridgid SR-20 NaviTrack or similar. You’re not going to buy one of these, but some tool rental places carry acoustic ground microphone kits for around $60–$80 a day. Results depend heavily on the user’s experience; on your first try you’ll probably hear a lot of confusing noise.
Thermal Imaging Cameras (FLIR)
A FLIR thermal camera can show temperature differentials in your floor that might indicate a wet spot under the slab. The FLIR ONE attachment for iPhone 11 was running about $249 on Amazon in 2021 and clips onto the Lightning port. Pair it with the FLIR ONE app and walk your floor slowly — a slab leak often shows up as a warm bloom in the floor surface if the leaking line carries hot water. Cold-water slab leaks are harder to spot this way.
Note: FLIR updated their lineup significantly and the pricing has shifted, so check current listings before you order.
When to Stop DIYing and Call a Licensed Plumber
Honestly, most of the above gets you to a confident “yes, I probably have a slab leak” — but confirming the exact location and depth requires professional equipment. A plumber with a proper electronic leak detection rig can pinpoint a leak within 6–12 inches, which is the difference between a small jackhammer cut and tearing up half your living room floor. Most plumbers who specialize in slab leaks charge $150–$300 for a detection visit, which is worth it.
Some plumbers also offer pipe re-routing as an alternative to breaking through the slab — they run a new line through the walls or attic instead of digging. Ask about this option if the slab repair estimate seems high.
Bottom Line
Apps and consumer hardware can help you confirm you have a problem and roughly narrow down the zone, but they’re not a substitute for a licensed plumber with professional acoustic and pressure equipment. Use the tools above to build your case before you call — you’ll have a more useful conversation and waste less time on the service visit.