The device that detonated beneath Ivan Watson and Ali Hamdani's car in Baghdad was what's known as a sticky bomb. But what exactly is a sticky bomb? Less than a month ago, The New York Times ran a great piece on the devices. From that article,
They are usually no bigger than a man's fist and attached to a magnet or a strip of gummy adhesive — thus the name "obwah lasica" in Arabic, or "sticky bomb." Light, portable and easy to lay, sticky bombs are tucked quickly under the bumper of a car or into a chink in a blast wall.
So that's what they look like. Here's a bit more on how they're constructed.
"You take a bit of C4 or some other type of compound," said Lt. Col. Steven Stover, a spokesman for the United States military in Baghdad. "You can go into a hardware store, take the explosive and combine it with an accelerant, put some glass or marble or bits of metal in front of it and you've basically got a homemade Claymore," a common antipersonnel mine.
Bombers detonate them remotely. The devices aren't a new innovation, as earlier versions were developed and used in World War II, and they've been used in Iraq for a few years. There's been an uptick in their use recently, however, and soldiers now receive training on the magnetic IEDs.