> Cell phone companies record the tower that handles each call, and then
> keep that info for at least a short time.
This has been S.O.P. for a long time, and that information is
generally kept for as long as your carrier keeps copies of your past
bills (in my case, at least 2 years, in the case of other carriers,
who knows ... perhaps forever?). The original purpose was for
maintenance reasons (logging cells that frequently drop calls, for
example) as well as fraud tracking (If your phone makes a call from a
cell in New York City, and then five minutes later, a phone claiming
to be yours makes a call in Montana somewhere, then fraud is
Of course, in our current era, these same logs are convenient for
investigators in they can potentially bolster a claim that you were
elsewhere than your purported alibi.
> That came out in the recent arson case in Maryland. The suspect
> claimed that he was at home. However, he had a cellphone call during
> his alibi time. His provider's records showed that the cell tower
> handling his call wasn't near his house.
Refuting the validity of this evidence to bolster the prosecution's
case depends on how far away that cell tower was. There are plenty of
reasons for a non-adjacent cell to take your call. Perhaps the
nearest cell was at capacity and could not handle your call, but your
phone happened to be able to pick up a not-so-nearby cell that had
Or, perhaps there was an odd atmospheric disturbance that permitted an
unusual propagation of radio waves to distant cell sites (similar to
listening to a distant radio station "on a skip"). Such an argument
tends to be less plausible the generally low-power nature of cell
phone transceivers, but such things could still happen under very rare
In any case, cell site records aren't a smoking gun. Even if you
happen to be making a call at a cell that covers the scene of a crime,
there can still be a rather wide area that the cell covers, anywhere
from a radius of a quarter of a mile (for microcells in dense metro
areas) to several miles (in rural areas). Such records may suggest
that your phone was in the area, but it won't always pinpoint you to
the exact spot. If you have a plausible alibi that puts you in the
vicinity of the crime but not connected to it, then the cell site
evidence could be moot.
Further, unless the phone has been tapped or a witness sees/hears you
using it, they still can't definitively prove it was YOU using the
> (Putting my tinfoil hat on:) I have a theory that the location of
> every cellphone that is turned on is being routinely recorded, say
> every minute, and saved for later data mining.
No, not every minute. For one thing, your phone when "idle" is not
constantly transmitting. To have everyone's phone constantly transmit
would really degrade battery life, and also severely cripple the cell
network as it is overwhelmed with broadcasting cell phones and not
enough channels to handle them all.
Cell phones do, however, register with the network from time to time
using a brief burst of data. They generally do this when a phone moves
out of a specific "zone" or cluster of cells into a new area,
broadcasting a "here I am!" message so that in case a call comes in, the
network knows in which cell group it will find your phone and cause it
to ring. And if a phone is sitting still, it might send out a
registration every 5-15 minutes or so to remind the network that it's
> I have no direct evidence. However, this is technically feasible,
> and is a logical (to me) extension of what we know was done decades
There is one last thing to note. All cell phones being sold in the US
are now FCC mandated to have a location-tracking capability built-in.
Most cell phones have a GPS-assisted device inside them now that
permits this capability, and with it you can theoretically be
pinpointed to within a couple hundred feet. However, this is
generally activated only when someone dials 911 and is connected to a
dispatch center that can retrieve that location data. The intent here
is to allow cell users to enjoy the same benefits as most landline
users when they dial 911 (emergency personnel can find you even if you
don't know where you are or otherwise cannot relay that information).
However, even now, not many 911 call centers can retrieve this info,
because the capability requires expensive upgrades that many local
governments haven't bothered to spend money on.
And in any case, both the traditional cell-tracking data and the more
precise GPS data can be easily circumvented: if you don't want to be
located, turn off your cell phone. :)
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