I have the same non-contact tester. It is very sensitive. I was at a friend's house helping him install a ceiling fan. We had the breaker off and used the non-contact to verify that the circuit was dead. When I got on the ladder to test in the ceiling box, the tester was going crazy. His wife had these lights hanging from the ceiling. The tester was picking up the magnetic field from them, even though I was 3 to 4 feet away from them.
This is the model I use at work I haven't had any issues with it giving false readings when it is around a lower voltage source. However, if you have enough static electricity, it will pick it up.