I have kept a cheap pocket knife in my backpack for the last three years of traveling and TSA has yet to find it. I don't do anything special, it's just sitting my my bag, and I fly maybe 10-20 times a year, domestic and international. It's definitely theater to a certain extent. Is there a nonzero chance of catching a bad actor? Sure, but it's not much higher than zero. They did find and confiscate a 3/8" driver socket wrench though because it was longer than 6". Thank God they kept that off the plane...