Is it possible to detect a mobile phone which is in stand by mode (non active)?

Yes you can detect it with our NF spectrum analyzer because even in stand by mode the charge pump and other electronic circuits within the phone are still working (at a very low level).

Anyway you would need a ultra senitive unit which can detect a view pT or even lower.
But we offer those :

The best unit to pick up such super low radiation (those circuits work in the kHz or MHz range) would be our NF-5030 with DDC (option 005).

If you want a even higher sensitivity you can add a external magnetic antenna to the analog input. Then you should be able to detect stand by phones even "quite far" away.

P.S. The iPhone 3G radiates a very nice signalmix incl. a lot of harmonics up to about 10kHz. Have a look at this long time recording snapshot we just made: