There's a phrase that resolves the doubt before the list of applications: The phone cannot detect gold.. It's not a matter of a better app or poorly adjusted sensitivity. The sensor these programs use is the magnetometer—the device's compass—and it only reacts to ferromagnetic materials, such as iron, steel, and nickel. Gold is not ferromagnetic. Silver, copper, aluminum, and bronze are not either. Physically, there is no signal to be read.
This doesn't make the magnetometer useless. It finds nails in walls, steel pipes, metal beams, hinges, and screws—useful things in the daily life of someone drilling a hole in a wall. This article explains what the sensor can actually do, what only a real metal detector does, how much this equipment costs, and what Brazilian law says about going around looking for treasure.
How the cell phone sensor works
The magnetometer exists in smartphones for a simple reason: to orient the map. It measures the surrounding magnetic field, using the Earth's field as a reference, which ranges from 25 to 65 microteslas depending on the region. When a ferromagnetic object approaches, it distorts this field, and the app displays the variation as a number or a graph.
That's why the range is small: the distortion disappears quickly with distance. In practice, the sensor detects a ferrous object a few centimeters away, and only if it has a reasonable mass. A nail inside the wall, yes. A wedding ring buried in the yard, no—not even if it were made of iron, because it would be too far away.
A side effect that confuses many people: speakers, cover magnets, headphones, speaker boxes, and the structure of the furniture itself also distort the field. Those who pass their cell phone across the table and see the number go up and down are usually detecting the drawer hinge, not a treasure.
Why gold is impossible for this sensor.
Ferromagnetism is a property of a few elements—basically iron, cobalt, nickel, and some alloys. Gold is diamagnetic: instead of being attracted, it is extremely weakly repelled by a magnetic field, at an intensity that no cell phone sensor can distinguish from the noise. That's why jewelers use the magnet test as one of the first filters against counterfeiting: a piece of real gold doesn't stick.
In other words, an app called "gold detector" faces a fundamental contradiction. The only sensor it has available is precisely the one that ignores gold. When the screen beeps, either there was something ferrous nearby, or the program is simply reacting to the device's movement.
How does a real metal detector work?
Professional equipment does not measure magnetic fields: it generates One. The coil emits an alternating electromagnetic field that induces electric currents—called eddy currents—in any buried conductive object. These currents create a secondary field, which the coil detects. Because all metals conduct electricity, this method finds gold, silver, copper, and aluminum, not just iron.
The most common models are of the VLF type, low frequency, with discrimination capability: they differentiate metals by the signal signature and allow them to ignore ferrous debris. Pulse-induced detectors penetrate deeper and work better in mineralized soil and wet sand, but discriminate worse.
Regarding price, the range is wide. Entry-level models for recreational use usually cost a few hundred to a few thousand reais; equipment with advanced discrimination, larger coils, and water resistance are well above that. None of them fit inside a phone, because they all need a coil, dedicated electronics, and their own battery.
What can you do with the app in practice?
- Locating nails, screws, and metal profiles in drywall walls, Before drilling, it works because the ferrous objects are only a few centimeters away.
- Finding steel pipe or metal conduit shallow. PVC pipe and live copper wire are not visible.
- Finding a dropped key or tool in tall grass or between cushions, as long as it is made of steel.
- Check if an object has ferrous parts., bringing it closer to the sensor.
- Interesting fact about electromagnetic fields. near electrical appliances, with the caveat that the magnetometer is not a calibrated exposure meter.
Here's a tip that greatly improves results: find out where the magnetometer is located on your model. It's usually on the top of the device, and that's the area you should pass close to the target, not the entire back.
Before you start looking: what the law says
Treasure hunting has rules in Brazil, and it's worth knowing them before buying equipment. Searching on someone else's property requires the owner's permission. Archaeological sites and items of historical value are protected by federal law and fall under the guardianship of historical heritage: excavating or removing pieces from these locations is an infraction, and there are penalties. Beaches, parks, and conservation units follow their own rules, defined by the managing body of each area.
The Civil Code also addresses the finding of lost property: whoever finds someone else's object must try to return it to the owner or hand it over to the competent authority. In practice, the metal detectorist community works with a simple code — ask for permission, repair the hole, collect any metallic debris found, and do not disturb a protected area.
What does a magnetometer actually find in a home?
With the impossible promise discarded, what remains is a legitimate and useful application — provided you know what to expect. The sensor detects magnetic field variation, So, he reacts well to:
- Nail and screw in a masonry wall, a few centimeters deep.
- Metal upright of plasterboard walls, which is where it really helps the most.
- Iron pipe and metal conduit.
- Rebar In slabs and beams, if they are close to the surface.
- Magnet of any kind, which is what he finds most easily.
And what did he no Based on physical principles, it considers: aluminum, copper, brass, gold, and silver, which are not ferromagnetic; PVC pipe; electrical wiring without current (although some applications detect the field of an energized wire, which is another matter); and any object buried more than a few centimeters deep.
For home use, there's an additional practical limitation: the sensor is located in a specific spot on the device, which varies by model. Discovering where it is—by slowly running the phone over a familiar nail—greatly improves the result.
How to use it without making mistakes
- Check the pressure beforehand. Make the figure-eight motion with the device, which is the gesture that compass apps require. Without this, the reading will be off.
- Take off the cover., Especially those with magnetic closures — they saturate the sensor and make any reading impossible.
- Stay away from sources of interference.Speaker box, motor, power panel, another cell phone, table with metal frame.
- Move slowly and in a straight line., observing the variation, not the absolute value.
- Confirm it in two ways. Pass horizontally and vertically; a real find appears in both passages.
- Mark with tape Instead of relying on memory, because the detection range is wide.
To drill a hole in the wall safely, the right tool remains the... detector with capacitive sensor, which finds wood, plastic and emptiness in addition to metal — and the voltage detector, For use around live wires. They are inexpensive and prevent accidents that cell phones don't.
Illegal mining and metal detection in Brazil: what the law says
It's worth knowing this before you start looking, because the subject isn't open-ended:
- Mineral resources belong to the Union. Extraction requires authorization from the competent authority, and there is a specific regime for artisanal mining, with permits and a defined area.
- Private land requires permission from the owner., in addition to the mineral title.
- Conservation unit and indigenous land They have their own regime and severe restrictions.
- Archaeological heritage is protected by law. Finding and removing objects from archaeological sites is an infraction — and the obligation, upon identifying such a find, is to notify the competent authority, not to excavate.
- Beach and marine area They are public goods, with their own rules of use.
Detection as a hobby, on one's own land or with permission, searching for a lost object, is another matter entirely—and it's the use that most people actually have in mind. It's important not to confuse this with the promise of finding gold with a cell phone, which is impossible for two reasons simultaneously: the sensor doesn't detect gold, and the range is limited to a few centimeters.
Frequently Asked Questions
1. How do metal detection apps work?
They read the magnetometer, the same sensor as a compass, and show the variation of the magnetic field around them. They don't emit anything and don't generate their own field.
2. Do they detect any type of metal?
No. Only ferromagnetic materials, such as iron, steel, and nickel. Gold, silver, copper, and aluminum are not detected.
3. What is the actual range?
A few centimeters, depending on the object's mass. There's no setting to increase this, because the limitation is in the sensor, not the app.
4. Do I need any additional equipment?
To find nails and pipes, no. To search for any buried metal with some chance of success, yes: a detector with a coil.
5. Is there a paid app that detects gold?
No. Paying doesn't change the physics of the sensor. Apps that promise this usually just display animations and ask for a subscription.
Conclusion
This "gold detector" app promises something that the phone's hardware can't deliver, because the only available sensor is blind to gold. What exists is a short-range ferrous object locator—useful for drilling a wall without hitting a pipe, and nothing more.
If the interest is genuine, the way to go is a detector with a coil, a bit of study on signal discrimination, and attention to the rules of where one can and cannot search. This way, the search remains true to physics and within the law—which is how it usually yields results.
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