The Infamous neonscrewdriver!
Not worth buying they don’t give a good indication of what’s happening, for not a lot more you can buy a cheap multimeter which will let you see more useful information and do tests with the power off -a lot safer!
The Neon screwdriver may appear to indicate no power when infact there is power such as if the sun is shining brightly so you cant see the neon glow, or your doing DIY in your wellies so you don’t provide the earth path needed for the neon bulb!
Anyway, you might think “I’ll buy one anyway, I can always use it to put screws in” don’t do it!! **they don’t even work as a screwdriver** the inside tends to slip round, which is most dangerous especially as the screws you are most likely to do with it are for electrics which need doing up tight!