A while ago there was a thread on flashlights in the technology forum. I used to travel with 3 or 4 flashlights, now, since I am trying to pack lighter and lighter I
just carry something like this or a Surefire light. Never had a problem with TSOs or their equivalent in a wide range of countries in North America, Asia, Africa, Europe or Australia. Flashlights are actually required on planes, and I have been on a commercial flight where they needed them for an in air emergency (before I carried one myself).