  An analysis of detector-efficiency in many-site Clauser-Horne inequalities is
presented, for the case of perfect visibility. It is shown that there is a
violation of the presented n-site Clauser-Horne inequalities if and only if the
efficiency is greater than n/(2n-1). Thus, for a two-site two-setting
experiment there are no quantum-mechanical predictions that violate local
realism unless the efficiency is greater than 2/3. Secondly, there are n-site
experiments for which the quantum-mechanical predictions violate local realism
whenever the efficiency exceeds 1/2.
