Finding the plumbing layout before breaking through the wall is the dream of any renovation project. And that's precisely why app stores are full of programs promising to see pipes through plaster, with convincing names and screens full of graphics. Before downloading any of them, it's good to know that most of these promises don't hold up.
Cell phones don't have radar, ultrasound, or X-ray. The only sensor with any relevance to the issue is the magnetometer—the same one used in compasses. It solves a small part of the problem. In this guide, we show what that part is, what features actually exist, and what the correct approach is when the service cannot go wrong.
What can a cell phone read inside a wall?
The magnetometer measures the magnetic field around the device, in microtesla. When ferromagnetic material is nearby—iron, steel, nickel—this field becomes distorted, and the application transforms the distortion into sound, vibration, or a pointer on the screen.
The useful range is short: between 2 and 10 centimeters, depending on the size of the part and the model of the device. Within this radius, it is possible to locate nails, screws, drywall studs, steel conduit, shallow metal junction boxes and, in older buildings, galvanized iron pipes very close to the surface.
It's not much compared to what's advertised, but it solves a good portion of household problems: finding the right amount is exactly what you need to safely hang a TV or a shelf.
And what he absolutely cannot do is...
The critical point: The magnetometer does not detect PVC, PEX, or PPR pipes.. Plastic does not respond magnetically, and that's precisely what the plumbing in most Brazilian homes is made of. A PVC pipe full of water is invisible to the sensor.
It also doesn't measure depth, can't distinguish a nail from an iron pipe, doesn't identify live wiring, and doesn't work on thick concrete walls. And it's easily fooled by magnets on phone cases, speakers, electrical panels, and metal furniture on the other side of the wall.
Regarding augmented reality apps that "show the pipe" on the screen: they draw over the camera image based on what you mark. There's no reading of the inside of the wall there—it's a visual annotation, useful as a record, but nothing more than that.
5 resources that really help.
1. Metal detector (Smart Tools co.)
Direct reading in microtesla
Free on Android, it's one of the most downloaded apps in its category and one of the clearest about its own limits. It displays the magnetic field value with an analog pointer and triggers an audible alarm when the reading rises, allowing you to sweep the wall without looking at the screen. View on Google Play.
2. Metal Detector (ExaTools)
Adjustable sensitivity and history.
Another free option for Android, with sensitivity adjustment — useful for distinguishing a small screw from a large one — and measurement logging, which helps compare two points on the same wall. View on Google Play.
3. Physics Toolbox Magnetometer
Raw data, without interpretation.
Developed by a physics education company, it displays the magnetic field graph on three axes and allows recording and exporting. It's the most reliable option for those who want to understand what's happening rather than just watching an animation. Free for android It is iphone. There is also the iPhone Smart Metal Detector, Free and simpler.
4. FLIR ONE
Attached thermal camera: only shows the hot water line.
Start with the limit, because it's significant: thermography can't see any pipes. It reads the temperature difference. on the surface From the wall, only what heats the plaster appears—that is, a hot water line with circulating water. Cold water PVC, which is precisely the case for those who are going to drill into the wall, remains invisible even to the thermal camera. Within this narrow scope, the only realistic way is via mobile phone, and it requires hardware: the app is free, but only works with the FLIR ONE thermal camera connected to the device. With the hot line in use, the trace appears regardless of the pipe material, and the camera also helps to locate moisture stains from leaks. View on Google Play.
5. Seek Thermal
Alternative thermography for mobile phones
Same logic as before, and the same limitation: Seek's thermal modules read surface heat, not the interior of the wall. The app is free and serves only as an interface for the accessory. It's useful for those who already have the equipment or are going to invest in it to hunt for hot water leaks and infiltration—not for mapping cold water plumbing. View on Google Play.
A method that truly reduces risk.
The app is just one layer. The sequence below prevents most accidents during a home renovation:
- Look for the plumbing and electrical plans. In new properties, they usually exist and can resolve your question in five minutes.
- Respect the prohibited zones: do not drill vertically above or below electrical outlets, switches, faucets, valves, and showers, nor in the horizontal strip next to them. This is where the plumbing goes up and down.
- Slowly run the magnetometer app over the magnetometer, without a case, with the compass calibrated, and mark with a pencil every point that gives a signal.
- Close the water supply and turn off the circuit breaker for the room before drilling.
- Drill a shallow hole first, gradually increasing the depth with the appropriate drill bit for the material.
- Photograph the exposed walls at any construction site. That photo is worth more than any app after the plastering has been done.
When to call in real equipment and real people.
For frequent home use, the right investment is a handheld wall detector. Models from Bosch, Stanley, and Vonder locate ferrous and non-ferrous metal, wood, and live wires, with depth indication—features that cell phones simply don't have because they depend on signal transmission.
If the problem involves a hidden leak, buried piping, or plastic tubing that needs to be precisely located, the service is provided by a company specializing in leak detection. The techniques used include electronic geophone, tracer gas, inspection camera with probe, and thermography. It costs significantly less than breaking down the wrong wall and redoing the finishing.
If the idea was just to visually plan the change, you can start from another angle: see how. Simulate wall painting using your cell phone. before touching anything.
FAQ
Q: Is there an app that can find PVC pipes in walls? A: No. PVC is not magnetic, and the cell phone doesn't have radar or ultrasound. And the attached thermal camera doesn't solve the common problem either: it reads heat on the wall surface, so it only shows the line of hot water in use. Cold water PVC pipes don't appear in any app.
P: So these apps are useless? A: No. They find nails, screws, metal studs, and steel conduit within a few centimeters. This already avoids a good portion of the problematic holes and helps to secure shelves and TVs in the right place.
Q: Can we completely trust the result? A: No. The app indicates the presence of metal, but it doesn't specify what it is or at what depth. Treat this as an indication, never as a definitive diagnosis.
Q: Do I need an accessory? A: For the magnetometer, no. For thermography, yes: the thermal camera is a separately sold module, and the app alone does nothing.
Q: Does it work on any wall? A: Best on drywall and thin plaster. On thick concrete, the sensor's short range doesn't reach what's behind it.
Conclusion
There's no app that turns your phone into a plumbing detector. What does exist is a magnetometer capable of pinpointing ferrous metal a few centimeters away, and a thermography option that requires a paid accessory. Knowing this, you use the right tool for each situation instead of relying on an impossible promise.
In practice: consult the project plans, respect the zones around electrical outlets and faucets, mark what the app can pinpoint with it, turn off the circuit breaker and water supply, and drill slowly. For larger projects, buy a wall detector. For leaks, call someone with a geophone and thermal camera. This way, the wall remains intact, and so does your wallet.
