  We consider the measurement of the third cumulant of current fluctuations
arising from a point contact, employing the transitions that they cause in a
quantum detector connected to the contact. We detail two generic detectors: a
quantum two-level system and a harmonic oscillator. In these systems, for an
arbitrary relation between the voltage driving the point contact and the energy
scales of the detectors, the results can be expressed in terms of an effective
detector temperature T_eff. The third cumulant can be found from the dependence
of T_eff on the sign of the driving voltage. We find that proper ordering of
the fluctuation operators is relevant in the analysis of the transition rates.
This is reflected in the effective Fano factor for the third cumulant measured
in such setups: it depends on the ratio of the voltage and an energy scale
describing the circuit where the fluctuations are produced.
