If you have a cell phone, "they" know where you are.

[rogerashton]

"In April the department produced invoices for military-grade spy gear that identify and track mobile phones in real time, Bloomberg Businessweek reports in its Oct. 20 issue. The department declined to say more, citing exemptions under the Homeland Security Act and the Arms Control Export Act. ..."

"At least 44 police forces across 18 states have mobile-phone surveillance gear, and others borrow it from federal agencies such as the Federal Bureau of Investigation or the Drug Enforcement Administration, according to the ACLU."

http://www.bloomberg.com/news/2014-10-16/local-police-tracking-mobile-phones-using-military-gear.html

[Jenoch]

1. The only way to defeat the tracking of a cellular telephone

is to remove the battery.

[AndyTiedye]

2. Only if the Cellphone is Turned On

If the phone is in airplane mode or turned off it isn't receiving or transmitting anything.

If they somehow got some malware onto your phone to make it stay on when it was supposed to be off, the battery drain would give this away pretty quickly (and removing the battery as suggested above would defeat even that).

[Jenoch]

4. Nope.

It is possible for the NSA to activate the microphone with the cell phone powerd down.

https://www.techdirt.com/articles/20130723/12395923907/even-powering-down-cell-phone-cant-keep-nsa-tracking-its-location.shtml

[AndyTiedye]

5. If the Phone Has Been Infected With Malware that Prevents it from Really Shutting Down, Yes

The article you linked also indicates that this capability most likely relies on previously-installed malware, which did in fact drain the batteries when the phone was supposed to be turned off (thus exposing the presence of the malware).

If one suspects that the software provided by the carrier contains trojans for the NSA, one could run AOSP on the phone if it is an Android phone. AOSP is open-source.

[HeiressofBickworth]

3. I've told this story before

but it is an example of the good/bad of cell phone tracking.

I was driving I-5 from Seattle to Olympia to have lunch with a friend. I got a flat tire somewhere around the south end of Tacoma. I called my friend to say I would be late for lunch, that I had a flat and I didn't know what I was going to do about it (hey, I'm an old woman and it's been forever since I changed a tire). She suggested I call 911 to get help. So, I called 911. I told the operator it wasn't an emergency but that I had a flat and was there some way I could get help. She said she could send a State Patrol car and the officer would help. I asked her if she wanted the milepost by where I was stopped. She said, "no, we already have you located." I was grateful that help was on the way, but a little freaked out that there was some way they had located me along the very busy freeway. I figured it had to be something about my cell phone.

[AndyTiedye]

6. GPS Location info for Cellular 911 Callers is Required

That is why all recent cellphones have GPS capabilities built in, it is required by law so that the 911 dispatcher knows where you are.
Presumably if you are calling 911, you WANT them to know where you are because you, or someone needs help.

Since the phones have that capability, they use it for a lot of other things, most of which you can disable.
Messaging and social media apps will tag your posts with your location if you let them, and sometimes this is on by default.
Same with camera apps.

Of course the cellular network knows where you are if you are using it, so do the police/FBI/NSA if they are taking an interest.