Jethro, would that apply to iPads and burner phones as well?
Any device that accesses the phone system. iPads do not.
"Burner phone" is a misnomer. Cell phones carry two globally unique identifiers. One is the IMEI and that is a number associated with the phone itself. The other is IMSI and that is a number associated with the SIM card in the phone. Those numbers are sent when phones connect to the phone network. Thus, law enforcement (or intelligence agencies) have the ability to track a phone and/or a SIM card and know such things as whether or not more than one SIM card was used with the same phone or if a SIM card was used in more than one phone.
Since such numbers are part of transactions with the phone network, including location information, a "burner phone" will show up. Consequently, a "burner phone" will give up where it is located and that phone can be correlated with other phones in the same location. Also, that "burner phone" will also show up for long periods of time in the same location which might reveal where the person with that phone lives or works. Even people being careful may use it inadvertently in the wrong place (their home, for example) or more likely someone calls or texts when they are in the wrong place which also yields location information.
The Geofence warrant is targeting Google because if you use your Google account on your phone, even if connected via WiFi, Google may end up with your location information as Google collects that whenever possible.
Your phone has on it a database of every Wifi and Bluetooth the phone has ever been in range of. The information in that database is sent upstream to the provider of the phone and some Apps have access to that database so it goes to them as well. This allows the ability to know a phone was in a specific location where the Wifi or Bluetooth was located. It is not required that the phone actually logon to such Wifi or bluetooth device, only that it is within range. With that information, various parties can learn that specific phones were all, at one time or another, within range of a particular Wifi or Bluetooth. This is how advertisers learn that your phone frequents a specific fast-food restaurant or frequents a particular grocery store, etc.
So, for example, MPD could go to Whataburger and find out the WiFi device identifier and then use that ID to try to find any phones that came within range of the Wifi on that day. If SWFA offers free Wifi MPD may be able to the same. Any other places on either side of 287 that offer WiFi can be checked because at a minimum it time-boxes a phone within an area in a specific time range.
Earlier on the threads I hypothesized that one avenue of investigation that may be worth looking at would be to go back to AT&T and see if they could identify phones that were likely off (or ran out of battery) prior to the murder (or Altima at SWFA) and came back on afterwards with a focus on phones that went off when the phone wasn't at "home" and a focus within that on phones that were in motion at speed (such as in a car) at the time it went off. Ideally, you would be looking for phones that went off while travelling in one direction and comes back on travelling the opposite direction. AT&T knows where the phone's "home" is even if you are not their customer just from location information alone as it is almost certainly the location where the phone spends the most time and they know if a phone is in motion and approximately how fast it is moving. Whether or not a judge would approve such a warrant is another matter.
All of this is meaningless if SP did not have a phone with them.
) my brain cells often get ahead of my typing fingers. 
