3.3V 5V Logic Signal Test Pen - Circuit Debugger

3.3V 5V Logic Signal Test Pen - Circuit Debugger. Thanks to its flexible probe, you can test the logic signal without using a multimeter. It is a pen. It is easy and fast to use. It has a red-green-blue LED on it that indicates the signal level. The red LED indicates high level, the green LED indicates low level, and the blue LED indicates that the signal is in the range of 0.6-2.4V or is not connected.