[Reaver]

Under the new matrix, your commlink doesn't directly connect you to an antenna "somewhere"...

Your commlink, when you go to make a call, connects you to the next closest device (Fred's commlink) and from that device to the next (Tom's commlink), and on and on down the line, around the world, to the person you are calling.....

A devices' sugnal range is tiny.... a few dozen meters, it is the presence of thousands upon millions of devices in a area that allows the matrix to work. Thanks to so many devices able to recieve and transmit, you get around the traditional bottlenecks that can happen in a wired system. (What we call PING now in gaming on computers).

But, the flaw in the system happens when you enter an area where there is no other devices to link together.... like in the middle of the ocean, or deep in the backwoods... (if i had a dollar for everytime we get a '411' assistance call to look for urbanite hikers, lost in the woods because they thought their iphone would lead them back out....)
Under such circumstances (being in the ocean/deep woods) your only hope of a matrix signal is a Sat uplink.

[adzling]

I'd go with the trace icon or bug scanner mechanics, possibly with a bonus as others have said.

I would ignore the RFID chatter however.

RFIDs come in various stripes but the tiny, cheap ones embedded in everyday objects are passive.
That is they do not emit anything unless activated by the specific radio frequency they are sensitive too.
This means you have to wave an RFID scanner at them or walk through an RFID door scanner to have them detected.

I.E. they do not transmit and so consequently do not cause noise.

[Gloubi]

After reading the few last posts, I think I'll handle that with using the Trace Icon or Bug Scanner rules, with a small bonus to the dice pool, as suggested.

Thank you all for your help and exhaustive answers

[Overbyte]

While it is theoretically possible, a friend of mine tried to do his master thesis on triangulating cellular antenna's - he failed. While it is mathematically possible the formula's were numerically unstable, meaning that a bit of noise caused a ripple effect that made the end result completely random.  Now I am not saying that it can't be done, I am saying that there is no documentation of such technology where cellphones triangulate a cellular antenna. My friend that is a brilliant student after a year and a half decided it cannot be realistically done.

I am a little confused by what your friend was trying to do, i.e. - "triangulating a cellular antenna", but I am 100% sure you can triangulate a cell phone transmission.

But in SR, since the matrix is presumably an ad-hoc network, its somewhat analogous to identifying the source of an internet "transmission". You have to trace the IP hops. Hence the analgous thing in SR is to run a Trace on the signal.

[korusef]

I was thinking about this, but that safehouse is in an isolated location with very low traffic ("Obscure/Difficult to Find" lifestyle-trait).
So "foreign devices" do stand out

In this case you won't even need the signal triangulation. Simply run Matrix Perception and you will automatically detect any new icons within 100 meters (unless they run silently) and you will know if there are "new" silent icons. But you will have to search for them separately.

Also to cover big area you need way more than 3 devices and you can still "defend" yourself by running silent (apparently running silent will mask your signal on hardware level):

Bug scanner: Also called a radio signal scanner, this device locates and locks in wireless devices within 20 meters. The scanner can also measure a signal’s strength and pinpoint its location. To operate a bug scanner, roll Electronic Warfare + Logic [Rating]. A device that is running silent (like a Stealth tag) can use its Logic + Sleaze to defend against the scan. If you get any net hits at all, you find the device. Wireless: You may substitute the scanner’s Rating for your Electronic Warfare skill when you use it.