What Exactly am I Measuring with an EMF Phone App?

I have an android phone app that uses the magnetometer on the phone (Keuwlsoft Gauss Meter). During sleep disturbances, mood issues/arguments, times of excessive pain, etc; If I turn on this app, I get high levels of EMF (60-200 Micro Tesla, WITH the phone in airplane mode, wifi, bluetooth off) During "normal" times, the levels will drop way down (usually 30-50 Micro Tesla). We actually had a recent incident where my little girl was unexplainably, unconsolably, highly emotional. At that moment, I began exploring with the app/meter, finding high levels inside (up to 150 Micro Tesla), but low levels outside (25-35 Micro Tesla). Just as I was about to video record the the difference, the levels inside dropped way down like flipping a switch. Suddenly my daughter was back to her smiling, happy self. The headaches, tingling feeling, etc we'd had during that moment went away too.

I tried to make a video demonstrating this phenomena. I assumed it was caused by radio waves. Transmitting with my walkie-talkie near the phone/app did not raise levels. I though it could detect EMF from radio waves, but no. But still, if I'm getting these spikes, what am I detecting, and, what kinds of devices/things could cause these spikes?

We live on a remote farm in the middle of nowhere with only 2 routers on the property. Ours is usually off and the closest one is in the landlord's house 80-100 feet away.

You are measuring magnetic fields and not radio frequency/microwaves.  My EMF meter measures magnetic fields in Gauss (G) and milligauss (mG) instead of Tesla or micro Tesla (uT).  A conversion chart shows that
1 Gauss = 0.1 uT.  Some research indicates above 2 mG is linked to illnesses like leukemia.

How dependable are the reads that you find using a smartphone app?  The smartphone itself gives off a significant magnetic field and if struggling to connect with a cell tower far away it will emit an even higher field - which may be the case if you are in a rural area far from a tower.

It's hard to say for sure where your extremely high reads are coming from without doing an EMF assessment of your property.  

https://www.emfanalysis.com/wp-content/uploads/2021/05/Biological-Effects-of-AC-Magnetic-Fields.pdf

https://www.emfanalysis.com/how-to-create-a-healthy-home/   

https://bioinitiative.org/ 

Phone application measure constant magnetic field, not ELF magnetic field, not electric field and not RF.
It is basically measuring the earth magnetic field.
The measurement is not relevant to EMF exposure or handing EHS.
Get a real meter to do real measurments.

It looks like there is an AC version of the app:

https://play.google.com/store/apps/details?id=com.keuwl.acmagneticfieldmeter

They do include this caveat:

"Magnetic field sensors will vary in sampling speed, resolution and accuracy from one device to the next. For indication only.

...

This app is designed for indication and educational purposes only. Always use a suitable calibrated more accurate device appropriate for the situation when required."

If you're only trying to determine if a wiring change reduced the ELF field strength in your house, this might actually be good enough.