You can check if the circuit is wired correctly. If you're unsure about the wiring, this is recommended as it allows you to check the answers for the Class 2 Electrician Skills Test practice. If the wiring is correct, the checker corresponding to the device will light up. Always use the included battery box for power confirmation. (Two AA batteries are required.) When connecting devices, make sure to connect L (black) and N (ground side) (white). This is a set with a pilot lamp checker that cannot be replicated with the HOZAN Pass Wiring Checker (Z-222) kit. Due to the pilot lamp in the photo being out of stock, only a green (green color) protective cover pilot lamp is available, and it will be difficult to confirm when lit, so it will be shipped with the protective cover removed. Therefore, the price has also been reduced. Thank you for your understanding. Pilot Lamp Checker Outlet Checker Hook-Ceiling Checker Lamp Receptacle Checker Construction Omission Checker Battery Box