A detector that is sensitive to static electricity.
Uses a CMOS 4000 chip like this circuit. When the detector is near an object with excess electron, the green LED lights up. Red LED lights up when it is near an object that has lost electrons. Both light up when the object is neutral.
cmos 4000 is dual 3-input NOR gate and inverter
resistors: 830 and 1200 ohms
This circuit was discovered by mistake by a student and it works very well.