Awesome project - Beautifully presented.
While you shouldn't use these tools in safety critical environments, you might like to consider adding a short section on how to use both this device as well as similar voltage detectors safely.
1. Use the detector to verify the presence of voltage in a known cable
2. Turn off the power to the known cable and verify that the detector indicates that
3. Use the detector to verify the status of an unknown cable.
And in all cases - even if a detector doesn't give an indication - assume that the cable is live :-)