  Fluctuations of the Hall voltage reveal information about long wavelength
magnetic field fluctuations. If gauge theories of strongly correlated electrons
are correct, such fluctuations are particularly large in the half-filled Landau
level and in high $T_c$ superconductors. We present estimates for the
magnitude, system size and frequency dependence of these fluctuations. The
frequency dependence contains information about instantons in the gauge field.
