How much location information can you get from cell phone caller ID?

February 13, 2015 11:40 AM

Is cell phone caller ID linked to the caller location, or to the area code? Is there a way to disable all location information?

I need to make some phone calls to people who already have my phone number, but as a matter of safety, I do not want them to know my physical location so I need to block this information.

Let's say my cell phone number is 617-XXX-XXXX (617 is a Boston area code). When I call someone else while I am physically in Boston, their cell phone displays that my number has called them from Boston, Massachusetts. Is that location triangulated information from my physical location, or is it derived from my area code?

In other words: if I were to travel to San Francisco and then call someone from this same number, would it display Boston or San Francisco? Can people using Verizon (the people I call, not me) derive the fact that I am in San Francisco from their phone bill? If this is the case, is there a way to block it?

posted by anonymous to Technology (8 answers total)

It is based on the area code (at least it was two years ago, as per my next paragraph):

I live in Minneapolis. My co-worker also lives here in Minneapolis, but his phone number was assigned to him while he lived in Missouri, and thus has a Missouri area code. Whenever he would call me before I put him into my contacts, it would always say Missouri on my caller ID even though he was physically living in and calling from Minneapolis.
posted by TinWhistle at 11:47 AM on February 13, 2015

I don't know anything about the technical details, but I can tell you that when my partner calls me (I have Verizon) from his West-Coast cell phone number while physically located in Boston, my caller ID says his phone number is from his West-Coast hometown.
posted by dorque at 11:47 AM on February 13, 2015 [1 favorite]

Same as TinWhistle -- my cell phone has an 865 area code (Knoxville, Tennessee), but I live in suburban Detroit. When I call people, it shows up as coming from Knoxville.
posted by Etrigan at 11:47 AM on February 13, 2015

Your cell phone carrier may have a way to block your caller ID information from showing up at all, or there may be an option in the settings on your phone to block caller ID, but instructions and options are very dependent on your phone and your carrier.
posted by jaguar at 11:50 AM on February 13, 2015

It sounds like the phone system transfers limited information

Number-only caller ID is called Single Data Message Format (SDMF), which provides the caller's telephone number, the date and time of the call. Name+number caller ID is called Multiple Data Message Format (MDMF), which in addition to the information provided by SDMF format, can also provide the directory listed name for the particular number. Caller ID readers which are compatible with MDMF can also read the simpler SDMF format, but an SDMF caller ID reader will not recognize an MDMF data stream, and will act as if there is no caller ID information present, e.g. as if the line is not equipped for caller ID.

So any phone that tells you the user's location is likely* telling you the location for the area code, which is nearly meaningless in this era of people traveling around the US with the same cell phone number.

You can always legally and freely block Caller ID information, or illegally spoof your caller ID (Wikipedia page with no direct links to such services). If you don't need to use your own cell phone, WikiHow has other ways of blocking or hiding your calling information.
posted by filthy light thief at 11:51 AM on February 13, 2015 [1 favorite]

Building off of Filthy Light Thief; one can block caller-id, but be aware that if you're calling a toll free number, ANI makes your number available. I'm not sure, but ANI also might allow your cell number to show up on the bill - as you're the originator, and the receiver doesn't handle tolling I suspect not. But it definitely won't include GPS coordinates, receiving cell tower coordinates, or similar. You have more to fear of social media linking your location than Caller ID.
posted by nobeagle at 12:27 PM on February 13, 2015

Just to add to the anecdata: my boss has a cell phone with an area code number from his previous residence, in Ohio. Anytime he calls me or I call him, whether we're both here in Virginia or sometimes when I'm in Virginia and he's over in DC, his location always shows as Ohio. Ditto the time I had to call when he was on vacation in Florida: the phone company still said he was in Ohio.
posted by easily confused at 1:15 PM on February 13, 2015

illegally spoof your caller ID (Wikipedia page with no direct links to such services)

Also, non-illegally, simply using a prepaid calling card—the sort that involves calling into a toll-free access number first and then entering a PIN and a destination number—may cause the caller ID information that shows up to be from whatever outgoing line you happen to be connected through. You could call yourself first to see what it looks like, though I suppose it's not necessarily guaranteed to be the same every time. (Theoretically the card company's computer system could forward your original caller ID info, but I haven't run across this myself.)

(And of course like other caveats above, the police or the NSA or whoever would still be able to figure out where a call came from.)
posted by XMLicious at 3:01 PM on February 13, 2015