Neon screwdriver is one piece of equipment that I always have somewhere in my house. It is great tool to check power sockets – put it in one hole, then another, if it lights there is some power. But that is not all. It can also double as a screwdriver! :)
Another thing I always have at home are my children. They are reason why all my power sockets these days have childproofing inserts. Since my home uses schuko sockets, insert is just piece of plastic that prevents inserting items in single hole. Only when both holes are touched simultaneously insert rotates a bit and allows for insertion of plug. That enables me to have protection for my kids and to insert plug without any tools or effort. Unfortunately this also means that I cannot easily use my neon screwdriver.
However, if you have two neon screwdrivers, things change dramatically. It is easy to synchronously insert both screwdrivers through holes and thus get reading. If socket is live, both of them will light up. Live one will light because your body is making connection (oven neon screwdriver) with live wire and neutral one will light up since your body is transferring little bit of current from live wire. If you have two identical neon screwdrivers you can see that neutral one is little bit dimmer.
However, you can just as easily remove one from socket in order to test other one. Remember that once screwdriver is in hole, protection will not close. As protection is open, continue tests as you usually would. Once both neon screwdrivers are out of hole child protection will close automatically.
P.S. Be very, very careful when dealing with live wires. Do not trust neon screwdriver. Test both of them on live socket first in order to see whether bulb still works.