Short answer: your phone's magnetometer â the compass sensor â detects the field distortion caused by iron and steel at a range of a few centimetres. That makes it useful for finding nails, screws, studs and pipework just beneath a surface. It cannot detect aluminium, copper, gold or silver, so it is not a treasure-hunting tool.
You can test your magnetometer right now with our free browser compass tool, or use the Metal Detector app which is built around exactly this sensor.
How Does a Phone Metal Detector Work?
Your smartphone has a built-in magnetometer (the sensor that powers the compass app). This sensor detects changes in magnetic fields caused by ferrous (iron-containing) metals. When you move your phone near a metal object, the magnetic field changes and the app alerts you.
đ§ Try it free in your browser
Magnetic heading from your phone's magnetometer, in the browser.
Open Online Compass âWhat Can You Detect?
| Material | Detects? | Why |
|---|---|---|
| Iron, steel, nickel | Yes | Ferromagnetic â distorts the magnetometer's field strongly |
| Studs in walls, rebar, steel conduit | Yes | Ferromagnetic fasteners and reinforcement inside them |
| Keys, tools, screws (steel) | Yes | Ferromagnetic, at close range (a few centimetres) |
| Gold | No | Non-ferromagnetic â produces no meaningful reading |
| Silver | No | Non-ferromagnetic â produces no meaningful reading |
| Aluminium | No | Non-ferromagnetic â produces no meaningful reading |
| Copper | No | Non-ferromagnetic â not reliably detected |
Try it on your own object with the Metal Detector app, which is built around this same magnetometer sensor.
How to Use the Metal Detector App
Step 1: Download the App
Get Metal Detector by Yalintech.
Step 2: Calibrate
- Move away from all metal objects and electronics
- Open the app
- Wave your phone in a figure-8 pattern
- Wait for the reading to stabilize
Step 3: Start Scanning
- Hold your phone flat (screen facing up)
- Move slowly over the area you want to scan
- Watch the gauge and listen for audio alerts
- When readings spike, you've found metal
Practical Uses
Finding Studs in Walls
- Calibrate the app away from the wall
- Slowly move your phone across the wall surface
- When you detect a spike, mark the spot
- Studs are typically spaced 16 inches apart â check for a pattern
Finding Lost Metal Objects
- Search systematically in a grid pattern
- Move slowly â about 1 inch per second
- Keep the phone close to the surface (1-2 inches)
- Mark detected spots and investigate
Checking for Metal in Packages
- Move your phone around the item
- Look for any magnetic field changes
- Useful for finding hidden components
Tips for Best Results
- Remove phone case if it contains metal or magnets
- Move slowly for better detection
- Stay low â detection works best within a few inches
- Avoid electronics â TVs, speakers, and computers create interference
- Use outdoors when possible â fewer metal sources to create false readings
- Multiple passes â scan the same area from different angles
Limitations
- Range: A few inches for small objects, slightly more for larger ones
- Non-ferrous metals: Gold, silver, aluminum and copper are not magnetic and will not produce a meaningful reading
- Interference: Electronic devices and building materials can cause false readings
- Not a replacement for professional metal detectors or stud finders for critical applications
Download Metal Detector on Android or App Store on iPhone.
