  Microlensing light curves are now being monitored with the precision required
to detect small perturbations due to planetary companions of the primary lens.
Microlensing is complementary to other planetary search techniques in its
potential for measuring the statistical frequency of planets beyond the solar
neighborhood. We present an algorithm to analyze the efficiency with which the
presence of binaries can be detected in real microlensing datasets. Such an
analysis is required in order to draw statistical inferences about lensing
companions. We apply the method to artificial (but realistic) data to explore
the dependence of detection efficiencies on observational parameters, the
impact parameter of the event, the finite size of the background source, the
amount of unlensed (blended) light, and the criterion used to define a
detection. We find that: (1) the integrated efficiency depends strongly on the
impact parameter distribution of the monitored events, (2) calculated detection
efficiencies are robust to changes in detection criterion for strict criteria
and large mass ratios, (3) finite sources can dramatically alter detection
efficiencies to companions with small mass ratios, and (4) accurate
determination of the blended light fraction is crucial for the accurate
determination of the detection efficiency of individual events. Suggestions are
given for addressing complications associated with computing accurate detection
efficiencies of real datasets.
