Leak detector alarm, no visible water: what to check

A leak-detector alarm that beeps while the floor still looks dry is a signal, not a puddle. The device noticed moisture, a splash, or a change at a sensor. It did not mark a pipe. Walk the likely wet spots, then read the meter before anyone opens a wall.

If you already have stains, a spinning meter, or a warm floor and no alarm in the story, start with signs of a hidden water leak. If you already know water is leaving and need the locate visit, that is how plumbers find a hidden leak. This page is the beep with a dry-looking floor.

What kind of detector sent the alert

Name the device before you name a leak. A puck on the floor, a rope or cable along a wall, and a whole-house valve at the main are three different alerts. They are not the same job.

A puck sits under a sink, beside a water heater, at a toilet, or in a laundry closet. It beeps when its contacts get wet. Some also send a phone alert. The floor around it can already look dry if the splash was small, if a towel caught it, or if San Diego’s dry air evaporated it.

A cable or rope sensor runs along a baseboard or around a heater pan. It can alarm from a thin film you would miss on tile. It can also alarm from mop water, a pet bowl, or condensate.

A whole-house unit sits on the incoming line, often near the garage shutoff or the meter side of the house. Some only notify. Some close a valve. If the taps went dead when the alarm sounded, you may be in a shutoff event, not a dry-floor mystery. Do not reopen that valve as a test. No water suddenly is the whole-house dry-tap path.

This page does not endorse a brand, a store gadget, or a claimed catch rate. No device accuracy figure is in our claims ledger, so none is stated here. Tell the plumber the type, the room, and whether the water is still on. That is the useful sentence.

Condensation fools puck sensors. A toilet tank sweats. A water heater in a closed garage sweats. An air-conditioner drain is not a supply leak. If the sensor sits against a tank or a pan that is only damp on the outside, say that. It still deserves a look. It is not automatically a slab leak.

What an alarm can and cannot confirm

An alarm confirms that the sensor’s threshold was crossed. It does not confirm a broken pipe. It does not confirm the leak is still running. It does not confirm the wet spot is in that room.

San Diego indoor air is dry most of the year. A cup of water on a Mira Mesa garage slab or an El Cajon laundry floor can vanish while you are at work. Vinyl plank and tile hide a film that carpet would show. A cabinet toe-kick can take the water sideways so the sensor’s floor looks fine.

The alarm also cannot tell a supply leak from a drain splash. A vanity puck will beep if the P-trap spit, if a kid overflowed the bowl, or if a supply line weeps. Those are different repairs. Your job in the first pass is to look, not to name the failed part.

A moving water meter can confirm that water is still leaving. The alarm cannot. If you want household signs without a gadget in the story, that list lives on the hidden-leak signs page. Do not treat this beep as a substitute for that list, and do not skip the meter because the floor looks dry.

If the alarm is in a Mission Valley condo, apartment, or townhome, the wet pipe may not be yours. Shared lines and HOA rules change who investigates. Read leak detection in Mission Valley before you authorize a wall cut in a stacked unit.

Where to look when the floor looks dry

Do this in order. The goal is a short report for a plumber, not a demolition.

1. Find the device that sounded. Look at its light or app if it has one. Note the room. Note whether it only beeped or also closed a valve.

2. Look at the sensor’s own spot. Lift it. Feel the floor, the cabinet lip, and the drywall paper at the baseboard. A faint dark edge is still a wet edge. Drywall can wick water up an inch and still leave the tile looking fine.

3. Open the nearby plumbing. Under every sink. The water heater pan and the drain from the temperature-and-pressure valve. The toilet supply and the tank. The laundry box and the washer hoses. The refrigerator line. You are looking for a drip, a crust, a swollen kickplate, or a warm, soft spot. Do not pull appliances out on a hunch if you cannot see behind them safely.

4. Listen with the house quiet. A hiss in a wall, a slab, or a water-heater closet is a reason to call even if the visible floor is dry. Do not keep running faucets to “make it show.”

5. Run a meter test. Turn off every indoor fixture. Skip irrigation. Skip the ice maker. Read the meter in the curb box, including the small leak-indicator triangle or star. Wait. Read it again. If that indicator still moves, water is leaving on the property side of the meter. If it holds, the event may have stopped, or the leak may be so small the wait was too short. Either way, you now have a fact the alarm did not give you.

City of San Diego single-family customers with a 3/4-inch meter pay a $35.53 monthly base fee as of January 1, 2026, and $8.51 per hundred cubic feet in the first tier. Other cities and meter sizes use different schedules. A spinning meter is still billed water. Oceanside, Helix, Otay, and other retailers are not that City of San Diego schedule. Read the agency on your bill.

If the meter moves, you do not need a bigger puddle to justify leak detection. If the meter holds and you found a splash zone at the sensor, you may have a one-time overflow. Watch it. If the alarm repeats with a still meter, say that when you call. Repeat beeps with no meter movement still need a look. They do not, by themselves, prove a hidden supply leak.

A high bill with no alarm in the story is high water bill, no leak. Use that page when the paper is the first clue. Use this page when the gadget was.

If you need to stop flow while you wait, how to find the main water shutoff is the valve map. Do not force a stuck gate valve.

How a device alert differs from professional leak detection

A floor sensor is a tripwire. Professional leak detection is a locate. They are not the same visit.

The plumber you hire for a hidden supply leak isolates zones, watches a gauge lose pressure, then traces sound, heat, or tracer gas to a marked spot. That method is the how plumbers find a hidden leak page. Bring the alarm history to that visit. Do not expect the gadget to replace the gauge.

Detection is meant to shrink the opening. Repair still needs an access hole. Finish restoration is a separate question. Ask to see the mark before anyone cuts drywall, tile, or a slab.

California’s C-36 plumbing classification covers water piping from the property owner’s utility meter side to the structure, plus repair and replacement of that piping. Individual contractor capabilities still vary. A plumber who locates supply leaks may not reset your sensor or your Wi-Fi hub. Say if you also need the gadget looked at, so the match is honest.

We connect you with independent licensed plumbers. We do not own listening gear, we do not hold the trade license, and we do not set the price. You contract with the plumber directly.

No official leak-detection price is in our claims ledger. Get a written locate scope. If the mark is under a slab, that repair path is slab work, not a puck replacement. If the mark is a supply in a cabinet, that may be pipe repair at a visible joint.

Lead-free rules apply when the work replaces piping that conveys water for drinking or cooking. California and federal standards define lead-free as no more than 0.25% lead, weighted average across wetted surfaces of pipes and fittings, and 0.2% for solder and flux. The plumber on site should use parts meant for potable supply.

Even work under California’s contractor license threshold can still need a plumbing permit. The exemption in Business and Professions Code section 7048 is $1,000 for casual, minor work as of January 1, 2026. It does not apply if the job is part of a larger operation, if contracts are split to stay under the cap, if someone advertises as a contractor, or if they hire another person to do the work.

How to request a leak detection referral

Tell us the pattern in one pass. Alarm sounded. Floor looks dry, or you found a faint edge. Device type: puck, cable, or whole-house shutoff. Whether the water is still on. Meter moving or holding, if you ran the test. City or unincorporated county. House, condo, or apartment.

That routes the request to a C-36 plumber who locates hidden supply leaks, not a drain cable and not a gadget installer.

Check the license at the CSLB license check. Search by license number, business name, or personnel name. The database is down Sundays 8 p.m. through Mondays 6 a.m. for maintenance.

Bring a photo of the sensor in place, the app screen if you have one, and the meter if it was moving. A garage water heater in Santee and a vanity puck in a Pacific Beach cottage are different rooms. Say which one you have.

Do not name a slab leak unless a plumber has marked one. “Alarm under the water heater, floor dry, meter spinning” is a better sentence than a guess.

When to call us

Call when a leak detector alarm sounded, the floor still looks dry, and you cannot tell whether water is still leaving, or when the meter is moving and you need a licensed plumber to mark the leak before anyone opens a finish. The licensed plumbers we send handle leak detection on that visit. Call us at (858) 400-4417 and we’ll connect you with a licensed plumber.