A diagnostic test/device used to categorize the presence or absence of a condition of interest is evaluated against a reference standard to assess its performance measures. In monitoring devices where an activity is monitored over a time period, a patient contributes multiple events in a temporal sequence. It is easy to characterize event detection in the presence of a reference standard, by sensitivity which is the probability of detecting the event given that the event has actually occurred. However, specificity, which is the probability of a non-event given that the event did not occur, is not easily decipherable as it depends on the time window. Instead, counting the false positives and reporting the rate of false positives per time period may be an alternative to look at device performance. I would like to discuss possible ways to evaluate such devices and possible performance measures to evaluate performance. Examples include Uterine Monitors.