A passive detector includes a sensor configured to sense an environmental parameter and to generate an output signal at an output of the sensor in response to the sensed environmental parameter. An energy scavenging circuit is coupled to the sensor, the energy scavenging circuit configured to convert a first voltage, V1, across the sensor to a second voltage, V2, where V2>V1. A discriminator is powered by the second voltage and is coupled to the output of the sensor. A nonvolatile memory is coupled to an output of the discriminator. The discriminator is configured to compare the sensor output signal to a threshold and, in response to the sensor output signal being above the threshold, to provide a programming signal at the output of the discriminator. The programming signal is configured to cause data to be stored or erased in the nonvolatile memory.