If this is the wrong group I'd appreciate a pointer to the right one!

I was wondering if it is possible to detect the presence of inactive
cell phones/wifi devices by detecting radio signals they emit. I
figure wifi would be the best bet because I guess cells dont broadcast
all that much when not in use, right?

Would there be enough output to find them? Would it be strong enough
to detect over a distance of say 100m? Could signals from multiple
devices be distinguished? Would the equipment be very expensive. Would
I get thrown in prison?

I am interested in triangulating and tracking the movement of phones
through a small area as a potential postgrad project.

Thanks.

On Tue, 08 Jun 2010 14:59:52 -0700, Pietro rearranged some electrons to
say:

If this is the wrong group I'd appreciate a pointer to the right one!

I was wondering if it is possible to detect the presence of inactive
cell phones/wifi devices by detecting radio signals they emit. I figure
wifi would be the best bet because I guess cells dont broadcast all that
much when not in use, right?

Would there be enough output to find them? Would it be strong enough to
detect over a distance of say 100m? Could signals from multiple devices
be distinguished? Would the equipment be very expensive. Would I get
thrown in prison?

I am interested in triangulating and tracking the movement of phones
through a small area as a potential postgrad project.

Thanks.

The cell phone providers already track the phones, not sure that you
would be doing anything new.

"Pietro" schreef in bericht
...

I was wondering if it is possible to detect the presence of inactive
cell phones/wifi devices by detecting radio signals they emit.
If inactive means 'switched off', then 'no'.

I
figure wifi would be the best bet because I guess cells dont
broadcast
all that much when not in use, right?
If switched 'on' they DO exchange info with their 'cell' from time to
time.
If left stationary they will do so less, but if in motion they will do
so more frequently.

Would there be enough output to find them?
2 Watts (for a cellphone) is more than enough!

Would it be strong enough to detect over a distance of say 100m?
Yes.

Could signals from multiple devices be distinguished?
That could be troublesome. I have only experience with analogue
signals.

Would the equipment be very expensive.
Analogue can be home-build

Would I get thrown in prison?
Depends on your country. Not here ( in the Netherlands ).

Gerard.