This could be due to poor grounding of the tester as well as low moisture levels of the operator testing. For the grounding, please confirm the tester is grounded. We supply two washers on the back of the tester at the two screw positions to help with grounding. For the moisture, you can try applying lotion as well as testing with your thumb. The lotion will help with the moisture and your thumb offers more surface coverage on the test switch.