In its first iteration, the annunciator system remote was powered by an 8-volt regulator (LM317) on the battery charging board. Both the sensor circuit (30 feet away, connected to the regulator through 40 feet of wire) and the Gunn oscillator were powered by this regulator. With this configuration the remote would occasionally lock to the ON state continuously after being tripped by a moving object, even though the object had passed out of the sensor's field of view. The system was not actually staying ON continuously, but was being immediately re-triggered after timing out, through some unknown feedback mechanism. The cause was finally traced to a voltage transient on the 8-volt power rail when the Gunn oscillator turned off. I never determined the exact feedback path, though I suspect it was through the D pin of the PIR sensor. The lockup issue was eventually resolved by relocating the regulator (changed to 78L08) to the sensor board, relocating the Gunn oscillator switching transistor (2N2907) to the battery charger board, and providing the Gunn oscillator with its own regulator (8.2-volt zener diode). The configuration shown in Figure 1 is the final, as-built, circuit.