  We study fluctuations of electric current in a quantum resistor and derive a
general quantum-mechanical formula for the distribution of transmitted charge.
For that we introduce a scheme of current measurement that involves a spin
$1/2$ coupled to the current so that it precesses at the rate proportional to
the current. Our approach allows the study of charge transfer without breaking
the circuit. We analyze a single channel conductor and derive electron counting
statistics for arbitrary relation between temperature and voltage. For a
perfectly transmitting channel the counting distribution is gaussian, both for
zero-point fluctuations and at finite temperature. At constant voltage and low
temperature the distribution is binomial, i.e., it arises from Bernoulli
statistics.
