  We study non-equilibrium magneto-transport through a single electron
transistor or an impurity. We find that due to spin-flip transitions, generated
by the spin-orbit interaction, the spectral density of the tunneling current
fluctuations develops a distinct peak at the frequency of Zeeman splitting.
This mechanism explains modulation in the tunneling current at the Larmor
frequency observed in scanning tunneling microscope (STM) experiments and can
be utilized as a detector for single spin measurement.
