art installation that detects nearby people/phones

hello there,

I've been working on an installation that will sense people walking by and react to their presence. The part of the project I am having issues with is the detection method.

I decided that it would be interesting to grab cell phone transmissions (such as calls/texts/wifi/bluetooth) and turn the intercepted data into movement in the installation. I am not picky about the accuracy of the readings, in fact the more wild and all over the place it is could be a good thing. But what I am looking for is evidence that a person with a cellphone (or any other device) is in the vicinity of the installation.

currently I've been building and testing a variety of RF detection circuits (from some tutorials on the web) but so far these circuits tend to detect me rather than the phone. I realize that different cellphones have different frequency ranges (between 800-2000 MHZ) so I have a feeling that if I want this to work I would need some way to detect that entire range. From what I understand about RF detection circuits, the range depends on a few factors, mainly the diodes and the antenna.

Considering the issues I've been running into and my time constraint, I am looking for another way to detect cell phone presence within ~5 meters. Any ideas you have would be greatly appreciated.

some things i've been toying around with in my head are grabbing a cheap router and retrofitting it as a detector, or building a circuit that can sense wifi or bluetooth transmissions. Although ideally I would still like the circuit to be able to detect the presence of calls or texts.

if you would like i can share the circuit diagrams for the detectors I have built, maybe there's something you'll see that I can not.

so to conclude, any ideas/products/sites/articles that you think might be helpful would be greatly appreciated!