anyway, has anyone here taken their Arduinos on board an airplane before? any issues with security?
I routinely travel with suspicious looking electronics with destinations around the world. When visiting customers I often carry-on un-finished prototypes, ICs in exotic packaging, test equipment probes, etc. Things that the highly trained security officers do not often seen. Something small like an Arduino will just look like any other PCB in the x-ray.
In the unlikely event you are asked respond with, “Oh that is for my halloween costume. It makes it light up.” No need for specific details.
One note: If your Arduino is going to be battery powered, you may not want to carry-on the batteries with you. Recent changes in regulations regarding batteries could cause some concern. Depending on your origin and destination there are limits on the size and kind of batteries you carry which are not permanently installed in a device.