The K-II meter was designed to find electrical wires behind walls. When electricity is flowing it generates a magnetic field. The K-II detects this magnetic field and alerts the user via LED lights. Since electrical current operates at either 50Hz or 60Hz the K-II is dialed in at 95% accuracy for 50Hz-60Hz although it can read up to 20kHz the accuracy falls off to less than 5%.
The sensing antenna on the K-II meter is actually built into the circuit board. It is a square spiral located mid-way on the bottom of the device. Popular belief is that the sensor is at the tip, however this is false. So when an investigator is holding the K-II meter and pointing it at something they are holding it wrong.
Since the K-II meters antenna is located mid-way on the bottom the proper way to hold it is tip-up with the bottom of the meter facing out from your body. As if you were holding it against the wall looking for electrical wiring. Or the same way you would hold a stud finder against the wall.
The K-II is a single axis meter. This means it can only read one axis of the 3-axis electromagnetic field. If you are just looking for EMF this is sufficient. If you are looking for direction or maximum strength you would need a tri-field meter.
Note about EMF phone apps. At least for the Apple iPhone they do not work. Apple has blocked the access to the built in EMF detection from developers. No developer can access it. Any app on the market is a hoax.
Paranormal investigators have been using the K-II for a long time now. I personally don’t use one in my ghost hunting adventures. I use a Tri-Field meter. Paranormal investigators need to be aware of their surroundings and identify devices that can generate low-frequency EMF. Not every instance of the K-II going off is paranormal.