You will only measure magnetic fields where there are magnetic fields if you use a device that is sensitive enough and has a wide enough frequency range to catch most of it (because it's expensive to have a device that catches everything).

Timestamps:
0:11 axes explanation
1:39 Telephone pickup coil explanation
2:26 Meterk MK08
3:42 Fuyi Fy876
4:49 K-II (so called genuine version)
6:19 Cemprotec 34
7:58 Erickhill RT-100
9:12 GQ-EMF-390-v2
12:56 K-II (so called fake version)
14:35 Cornet ED88T
17:39 Trifield TF2 (standard mode)
19:05 Trifield TF2 (weighted mode)
20:37 EMFields PF5 Pocket
23:47 Gigahertz ME3830B
26:17 Gigahertz ME3851A
29:46 Results preface
29:52 Results

If you want to buy an EMF meter, I highly recommend to watch ALL the videos in this series before making a final conclusion and decision.

--Ghost hunters-- The K-II EMF detectors with their coffin like design, seem to be popular among so called "ghost hunters". If we read the bible, it's possible that so called "ghosts" are demons (aka falling angels). Can you measure them with a K-II EMF detector?

a) Yes.

b) Not exactly.
Entities may just trigger a detector to draw peoples attention. This may be one reason why some scientists deny the existence of "ghosts", because they likely won't trigger anything if they don't want to. People may think it's ok to play with "ghosts", but you may end up with "ghosts" playing with you, you may be harassed for some time after your adventures. Even if science would be able to measure "ghosts" in some way, they would probably deny they can and likely would not want to publish proof of that, to avoid making people believe a God could exist (god forbid), which is definitely against their evolution religion.

Also don't underestimate the deceptive skills of human kind. Some would probably sell their soul to the devil to get more views. A lot of videos may be fake by design, they may just make the device react by some kind of trick, maybe some strong source behind a wall or just behind the camera or they measure in a creepy place under high voltage power lines or something.

Don't underestimate the ignorance of human beings. Some may just be measuring some wiring error or something which can cause strong magnetic fields quite some distance. Inside a house with no power you could even measure something from outside in some cases.