The autocorrelation function of spectral determinants (ASD) is used to prob
e a system of disordered electrons. It is represented as an effective parti
tion function, and thus the problem is reduced to finding the spectrum of t
he respective effective Hamiltonian. A spectral gap above its ground state
is argued to be a strong indication that all states are localized. This met
hod is demonstrated for electrons in a quasi-1-dimensional disordered metal
wire as a function of a magnetic field, and for two-dimensional disordered
electrons in weak and strong magnetic fields.