  The sensitivity of experiments looking for annual modulated signals is
discussed and analyzed. The choice of energy intervals for rate integration and
enhancing the signal-to-noise ratio of the predicted WIMP signal is addressed.
Special emphasis is placed on quantifying the minimum required exposure, MT,
under experimental conditions. The difficulty reduces to establish the proper
separation between the rate due to the unmodulated part of the WIMP signal and
the rate of spurious background present in any experiment. The problem is
solved by placing an upper bound to the unmodulated part of the signal using
the best exclusion plot. We find that the lowest backgrounds achieved result in
exposures in the range MT ~ 5 - 100 kg yr for masses m_{\chi} > 100 GeV
depending on the energy threshold of the detector. While our results are valid
for Ge and NaI detectors, the formulae derived apply to other elements as well.
Prescriptions are given to estimate exposures for higher background
experiments.
