Re: is it possible to electronically and indiscriminately tag or ID cellphones.

Hi Philbert,

This is a an interesting question.

There are a number of challenges to overcome. First, you need some
way of uniquely identifying a phone. The problem is that there are
many different mobile phone technologies in use throughout the world.
Since you are from Kenya, I would guess that GSM is the prevailing
standard there. GSM uses a SIM card to identify a phone and it's
phone number. This is convenient because a user can simply take the
SIM card out of one phone and transfer it to another phone. That
way, it's easy to switch phones. The problem is that someone can
steal your phone and use it very easily!

You could build a circuit that could be added to the phone that
is enabled somehow. The problem is how do you identify the stolen
phone? If the original SIM card has been replaced, it's difficult,
if not impossible to contact the phone using the old number. Some
phones contain a unique identifier, but if you don't know it, it
won't do you any good. Most mobile phone carriers don't track that
number, so there's really no way to find the phone using the mobile
phone network.

We could look at it the other way: if we can't identify the phone,
can the phone identify itself? If the phone knew it was stolen, it
could automatically make an outgoing call to some fixed number.
That doesn't tell you much about where the phone is. Many phones
today include a built in GPS receiver, so it is theoretically
possible for the phone to tell someone where it is, but that requires
significant reprogramming of the phone software, which is not easy
to do.

Another option is to use tagging technology such as barcodes or
RFID. Barcodes are simple and easy to apply, but they are also
easy to remove. Radio frequency identification (RFID) tags are
now gaining momentum as an effective way of identifying products
using short range radio communications. You can read more about
RFID here:
 http://en.wikipedia.org/wiki/RFID

Many RFID tags are small and cheap. It's likely you could fit
one into a phone for identification later.
Of course, you would have to have possesion of a phone to determine
if the phone was stolen. I'm not sure that's possible in your case.

I hope that answers your question.
If not, please submit a more detailed question and hopefully I can
give you a better answer.