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Quick answer from a licensed plumber: For checking walls, floors and ceilings after a leak, the General Tools MMH800: it has pins and a pinless pad, and General Tools names locating water leaks as a use. For scanning a big area without holes, the Klein ET140 pinless meter, which reads up to 3/4 inch deep. For a simple pin meter, the General Tools MMD4E or the pocket-size Klein ET150. A meter shows where the water went; it does not show you the broken pipe.
Our pick for most leak checks: the General Tools MMH800 pin/pinless moisture meter. Check the General Tools MMH800 on Amazon
After a supply line, drain or fixture leak, the question is how far the water went: into the drywall, the subfloor, the ceiling below. A moisture meter answers that without tearing everything open. This page compares four meters, pin and pinless, that Amazon.com sold when we checked. Every spec and every leak-finding use on this page comes from the makers’ own pages and manuals.
If you have not found the leak yet, start with our guide to finding a water leak. If you want an alarm that catches the next one, see our water leak detector picks.
Moisture Meters Compared
| Meter | Type | Building materials range (maker) | Accuracy (maker) | Extras | Power |
|---|---|---|---|---|---|
| General Tools MMH800 | Pin and pinless pad | 1.5 to 33% | ±3% pin mode (page); ±(3% of reading + 5 digits) (manual) | Temperature and humidity | 9V |
| Klein ET140 | Pinless, up to 3/4 in. deep | 0 to 100% relative | Wood ±4%; drywall relative | Bar graph, tone | 9V |
| General Tools MMD4E | Pin, 0.3 in. | 1.5 to 33% | ±2% | Calibration check cap | 9V |
| Klein ET150 | Pin, 0.38 in. | 0 to 100% relative | Wood ±2%; drywall relative | Work light, calibration check cap | 2 AAA |
Figures from the General Tools MMH800 and MMD4E pages and manuals and the Klein ET140 and ET150 pages and manuals. Each linked meter was sold by Amazon.com and in stock on October 6, 2026.
Pin vs Pinless: What the Makers Say
- Pin meters read the moisture between two pins pushed into the material. General Tools says pins are the better option when accuracy matters because they detect moisture below the surface, but that on hard materials like wood or concrete, the reading mostly reflects surface moisture. The MMD4E manual says to push the pins in at least a quarter of the material’s thickness for an average reading.
- Pinless meters read through the surface without marking it. Klein says its ET140 reads up to 3/4 inch deep and gives an average, relative value, with moisture near the surface counting most. If the material is thinner than 3/4 inch, the reading may come from what is behind it.
- Both in one: the General Tools MMH800 has pins on top and a pad on the back, and its manual says the pad is the only choice for surfaces you cannot mark with pinholes.
How to Use One After a Leak
- Set the mode. Pick the drywall, building materials or wood mode that matches what you are testing; each maker sets its modes by material.
- Take a dry reading first. Klein calls its drywall and masonry readings relative, so a reading from a dry part of the same wall gives you something to compare against.
- Grid the area. The MMH800 manual says to take readings at different spots; the leak is where the meter shows the highest reading.
- Confirm with pins. Plumber’s note: a pinless scan finds the wet area fast, and a pin reading in a hidden spot, like behind a baseboard, confirms it.
- Recheck as it dries. General Tools says the MMD4E helps you decide whether to dry the existing materials or replace them.
Plumber’s note: the wettest spot is where the water ends up, which is not always where it gets out of the pipe. A meter tells you where to open up; it does not replace finding the leak. If it is a copper pinhole, our pinhole leak guide covers the repair.
General Tools MMH800 Pin/Pinless Moisture Meter with Temperature and Humidity
Pin and pinless pad sensors · wood 5 to 50% WME, building materials 1.5 to 33% · ±3% in pin mode on General Tools’ page; ±(3% of reading + 5 digits) in the manual · also reads air temperature and relative humidity · audible and visual low, medium and high alerts · hold button · 9V battery · hard case and two extra pairs of pins (10 mm and 15 mm)
General Tools says the MMH800 is ideal for locating water leaks and measuring the moisture content of drywall, plastered walls, floors and subfloors. It has both sensor types: a pair of pins on top and a split metal pad on the back. Its manual explains when to use each. The pad is the only choice on surfaces you cannot mark with pinholes, like finished wood, paint or wallpaper. The pins are the better option when accuracy matters, because they detect moisture below the surface that the pad cannot.
The manual’s leak advice is simple: to find the source of a leak behind wood, plaster, drywall or a ceiling, take readings at different spots, and the leak is where the meter shows the highest reading. Its beeper speeds up as the reading rises, which General Tools says makes it easy to pinpoint the wettest area. It also reads air temperature and relative humidity on a second display, and General Tools calls it particularly suitable for water damage restoration for that reason.
- Pin and pinless sensors in one meter
- General Tools names leak location as a use
- Beeper rate rises with moisture level
- Temperature and humidity on a second display
- ±3% in pin mode on General Tools’ page (3% of reading plus 5 digits in the manual), against ±2% on the MMD4E
- On hard materials the pins read mostly surface moisture, per the manual
- No pinless depth figure in the General Tools documents we read
Verdict: The one meter to buy for checking walls, floors and ceilings after a leak.
Klein Tools ET140 Pinless Moisture Meter
Pinless (electromagnetic field) · reads up to 3/4 in. deep · modes for drywall, masonry, hardwood and softwood · drywall and masonry 0 to 100% relative · wood accuracy ±4% · nine-LED bar graph and alert tone · hold and auto power off · 9V battery · 6.6 ft drop protection
Klein says the ET140 detects relative moisture from leaks and flooding without making a hole. Its manual explains how: it reads the material’s capacitance through an electric field from the back plate, to a depth of up to 3/4 inch, and shows an average, relative value. Moisture near the surface counts for more than moisture at the full depth. Klein calibrates it for drywall, masonry, hardwood and softwood only.
Klein’s manual adds a catch. If the material is thinner than 3/4 inch, the reading may come from something behind it rather than the material itself. Plumber’s note: on a finished wall, a pinless reading can pick up whatever sits behind the board, so treat a high spot as a place to look closer, then confirm with pins. Klein also says the meter is not insulated, so keep it away from energized parts.
- No holes in drywall, masonry or wood
- Reads up to 3/4 in. deep, per Klein
- Bar graph and tone flag wet readings
- Built to survive a 6.6 ft drop, per Klein
- Drywall and masonry readings are relative, not a percentage of moisture
- Thin materials can read what is behind them, per Klein
- Not insulated; keep it off live parts
Verdict: The meter for scanning a large area of wall, floor or ceiling without marking it.
General Tools MMD4E Pin-Type LCD Moisture Meter
Pin type, 0.3 in. pins · wood 5 to 50% WME, building materials 1.5 to 33% · ±2% · low, medium and high tones and icons · cap doubles as a calibration checker · hold button · 9V battery · 1-year limited warranty
The MMD4E is a plain pin meter. General Tools says its pins find the moisture content in wood or drywall, to help you decide whether to dry the existing materials or replace them. It has a wood mode and a building materials mode, and in building materials it marks 1.5 to 16.9 percent as low, 17 to 19.9 as medium and 20 to 33 as high.
Two notes from the manual matter on a leak. Push the pins in at least a quarter of the material’s thickness for an average reading, and do not measure a surface with standing water on it, because that throws off accuracy. The pin cap doubles as a calibration check: with the pins in its holes, the meter should read 18.3 percent, plus or minus 1, in wood mode.
- ±2% accuracy, per General Tools
- Built-in calibration check in the cap
- Clear low, medium and high bands for building materials
- Replacement pins available
- Pins leave small holes
- No pinless mode
- 1-year limited warranty
Verdict: A simple pin meter for confirming what a pinless scan or a stain suggests.
Klein Tools ET150 Pin Moisture Meter
Pin type, 0.38 in. pins · modes for hardwood, softwood, drywall and building materials · drywall and building materials 0 to 100% relative · wood accuracy ±2% · color-coded backlit display · work light · cap doubles as a calibration checker · 2 AAA batteries · 6.5 ft drop protection
Klein’s ET150 is a slim pin meter with a pocket clip. Klein says its stainless steel pins help identify leaks, water intrusion and flood damage, and its color-coded backlit display shows low, medium and high readings at a glance. A built-in work light helps in dimly lit work areas, per Klein, and the top of the cap works as a calibration check.
Klein lists ±2 percent accuracy on wood and relative readings on drywall and masonry. Its manual gives the pin size as 0.38 inch; its product page says the pins penetrate up to 8 mm. Like the ET140, Klein says it is not insulated.
- Pocket size with a clip, per Klein
- Work light for dark spaces
- Color display for high, medium and low
- Calibration check in the cap
- Drywall readings are relative
- Pins leave small holes
- Operating range 50 to 104°F, per Klein
Verdict: A pocket pin meter for checking cabinets, baseboards and subfloors in dim light.
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Before You Buy
- Pick the sensor for the surface. Pinless for finished walls, floors and trim you do not want to mark; pins when accuracy matters, per General Tools, though its manual says pins in hard materials like wood read mostly surface moisture.
- Check the modes. Each meter here has a mode for drywall or building materials; readings in the wrong mode are not comparable.
- Read the scale. Klein’s drywall readings are relative; General Tools gives building materials a percentage with low, medium and high bands.
- Look for a calibration check. The MMD4E and ET150 caps double as calibration checkers, and the MMH800 pin cover does too, per its manual.
- Mind the wiring. Klein says its meters are not insulated.
FAQ
Can a moisture meter find a water leak?
It can show you where a wall, floor or ceiling is wet. The MMH800 manual says to take readings at different spots and that the leak is where the meter shows the highest reading. It does not show you the pipe; you still have to open the wall or trace the water to its source.
Pin or pinless: which is better for leaks?
Use both if you can. General Tools says a pinless pad is the only choice on surfaces you cannot mark, and pins are better for accuracy because they read below the surface. Klein says its pinless ET140 reads up to 3/4 inch deep, but thin materials can read what is behind them.
What reading means drywall is wet?
It depends on the meter. General Tools’ MMD4E marks 20 to 33 percent as high in building materials mode, and Klein’s ET140 lights its red LEDs at 70 percent and up in drywall mode. Klein calls its drywall readings relative, so compare a reading with one from a dry part of the same wall.
Can I use a moisture meter near electrical wiring?
Be careful. Klein says its ET140 and ET150 are not insulated and to avoid contact with areas where energized conductive parts may be present. Plumber’s note: shut off the circuit before you push pins into a wall near outlets or switches.
How do I know my moisture meter is accurate?
Use the built-in check. The MMD4E and ET150 caps double as calibration checkers; General Tools says the MMD4E should read 18.3 percent, plus or minus 1, in wood mode on its cap. If it does not, contact the maker.
Why Trust Plumbing Picks
Plumbing Picks is written by a licensed Georgia journeyman plumber. Every spec here comes from the maker documents linked below, or from the Amazon listings we link; nothing comes from hands-on testing. On October 6, 2026, every linked listing was in stock and sold by Amazon.com. If you buy through a link we may earn a commission at no extra cost to you. Nobody pays to be included here. More on who writes this and how we pick.
Sources
- General Tools: MMH800 pin/pinless moisture meter with temperature and humidity, MMH800 user’s manual
- Klein Tools: ET140 pinless moisture meter, ET140 instruction manual
- General Tools: MMD4E pin-type LCD moisture meter, MMD4E manual
- Klein Tools: ET150 pin moisture meter, ET150 instructions
- Amazon listings for each linked meter (linked above)
Bottom Line
Buy the General Tools MMH800 if you want one meter for leak checks: pins for accuracy, a pad for finished surfaces, and humidity on the side. Buy the Klein ET140 to scan a large area without marks, and the MMD4E or ET150 if a pin meter is all you need. Take a dry reading first, map the wet area, and find the leak before you close anything up.