Systems, circuits, and methods are described for providing efficient, monitoring capabilities for providing output reactive to monitored conditions. According to the disclosed methods, steps are included for providing a floating gate monitoring circuit in association with a monitored circuit and programming the floating gate to a selected charge level. The programmed floating gate charge level is then compared with a signal level in a monitored circuit. In an additional step, selected comparison criteria are used for selectably activating output. Exemplary embodiments of methods and associated circuits and systems employing the methods are also disclosed, in which protection for a monitored circuit is provided in the event of undervoltage, undercurrent, overvoltage, or undervoltage. Configurations of preferred embodiments of circuits, systems, and methods using the principles of the invention are disclosed in which ultra-low power is consumed by operation in an “ON” state, and little or no significant power is consumed when operating in an “OFF” state.