I have witnessed this more than once, particularly with the Ghost Meter and K-2 EMF Meter. On an investigation, 3 ghost meters were placed on a table. One meter kept going off while the other two remained silent. The investigator in order to try to prove that it was something paranormal affecting the meter, decided to change the position of all three meters. Again the same meter was giving an indication. The investigators concluded that it had to be a ghost that was causing this anomaly, because only one meter indicated the presence EMF field.
What I think is really happening is that the meter indicating the presence of an EMF field has a weak battery. In my career as an Aircraft Mechanic, I would use a digital multimeter everyday. I noticed sometimes times when taking a reading, the meter wouldn’t settle on a particular value. The meter reading would fluctuate wildly up and down. This was an indication that the battery in the multimeter needed to be changed. As soon as the 9 volt battery was changed, the meter would act normally.
I think this is the cause when a Ghost Meter or K-2 Meter starts giving a constant indication. If you have two EMF meters and one keeps going off, change the battery. If the indication persists, then maybe you have something paranormal. If the constant indication quits, then check the battery voltage to verify you have a weak battery.