Electromagnetic Field (EMF) detectors are popular pieces of ghost hunting equipment. The idea is that paranormal apparitions emit a noticeable EMF that proves their existence. But in reality, those EMFs come from electric and electronic devices. And an EMF from you microwave may, for example, interfere with your Wi-Fi network and cause performance problems. So you may want an EMF detector to diagnose such issues and Mirko Pavleski designed a DIY unit you can build.
This DIY EMF detector is sensitive to electromagnetic radiation and will indicate the strength of any detected fields. A display shows the relative strength of the detected radiation and a buzzer sounds at different frequencies that correspond to the strength, kind of like a Geiger counter. There is almost always some ambient EM radiation around us at all times, so this device adjusts itself at startup to set that as the baseline. Only EM radiation stronger than that baseline will trigger the device.
To keep the build as simple as possible, Pavleski chose an Arduino Nano board. The antenna, which is just a small piece of copper pipe, connects directly to an analog input pin. Other than that, the only components are a buzzer, an OLED screen, and a 9V battery wired through a power switch. Any EM radiation will induce a tiny current in the antenna, which the Arduino’s analog pin can detect. The stronger the EMF, the greater the voltage on that pin.
Most EM radiation is very weak and this isn’t the most sensitive device, but it should still be enough to, for instance, detect a live wire in a wall.