NOTE:
(1)Regarding product compatibility: it is NOT suitable for LED Christmas lights, it is suitable for incandescent lights, strip Christmas lights, mesh Christmas lights, ice-cream Christmas lights and so on.
(2)You have to take each bulb out to test.You have to take each bulb out to test,testing it individually.
(3)Take out the battery insulation sheet and check.
whether 2 button cells are correctly installed referring to negative and positive poles.
(4)After use, you need to turn the switch to OFF and switch off the tester to avoid the battery out of power supply.