re: What triggers TSA checked bag random search?

Who knows. Maybe when the scanner picks up something other than soft clothing and a shaving kit, the trigger happens. I've gotten sheets of paper, from the TSA, thrown in my luggage informing me that it had been searched.

I've flown with diving gear and at least 2 times, my dive knives attached to my BCD were taken. Furthermore, I've had other small objects come up missing.

I eventually printed up a sign that was attached to the inside of my bags that said, "DON'T STEAL MY shite!"