A power meter generates a time series of observations of power drawn by a device configured to operate in an active mode and to transition through a sequence of inactive modes comprising one or more intermediate inactive modes each having a bounded time duration terminating in a final inactive mode of unbounded time duration, and further configured to transition from any of the inactive modes to the active mode in response to a device activation signal. An electronic data processing device is programmed to determine statistical characteristics of the power draw of the device in each of the inactive modes by fitting a state model to the time series of observations. The state model represents each intermediate inactive mode including its bounded time duration and further includes a probabilistic representation of the transition from any of the inactive modes to the active mode in response to a device activation signal.