I watched a movie last night on TV. I don't remember the name of the movie, but it starred Jodie Foster as a propulsion engineer. The movie was about a complicated extortion plot that involved killing Jodie's husband so a bomb could be smuggled onto an airliner in his coffin, and then kipnapping Jodie's daughter on the plane so Jodie would create havoc searching for her daughter. The villians were the air marshall and one of the airline stewardess's. The point that struck me was the bomb. It had flashing lights on it. The bombs on the TV show "24" also feature flashing lights. I don't know anything about terrorists bombs, but it seems unlikely to me that flashing lights would be needed. My guess is that the movies need them for dramatic effect. When I was young back in the pre-solid state electronics era, the terrorist bombs used alarm clocks as the trigger mechanism. That made some technical sense then, and would still work. For dramatic effect the hero always de-fused the bomb just before the alarm was set to go off, with just a few clicks to go. The bomb in the Jodie Foster movie was quite small, and could have contained only a few ounces of an explosive like C4. Jodie, being an engineer, realized that, and used that knowledge to kill the villian with the bomb without killing herself, though it devastated the airplane, which was on the ground by that time.

My impression is that terrorists nowadays use cell phones to trigger bombs. That works, but I would still want a safe-and-arm device with a mechanical block on the ignition train. Without that, it would be embarrassing if someone called the cell phone number by mistake. I've had two wrong number calls on my cell phone in the past week, so it can happen. I read about terrorists blowing themselves up with their own device about once a month. Since those guys plan on killing themselves anyone, maybe the terrorist leaders don't think an S&A is cost effective.