When my brother was doing Op-For at camp Irwin he used one of the sensors from a garage door for simulated IEDs. Pressure plates, lasers, motion sensors, you name it and it'll make something go boom.

This is why IEDs are so effective in asymmetric warfare. They are cheap and anyone can get parts =(

I assume you're talking about the safety beams that prevent the door from closing on obstacles. Have you ever had the door go down on command and then halt, without any obstacle in the way? They're very noisy sensors - lots of false positives, not the sort of thing you want to wire up a massive bomb. They also actively emit light, so not very stealthy.

The first time I saw the results of an IED blast was a day after I arrived in Iraq. I had to shake a tree in order to retrieve the trousers of the guy who blew himself up planting the thing. That happened a lot. Making IEDs isn't very hard, but making a lot of them without eventually blowing yourself up is.

Or they simply use long wire buried in sand.

I only saw that a couple of times, in one case we caught the guy - he still had the 9v in his pocket (why he'd keep it I don't know). If you watch their videos you see that they prefer to be much further back than what is practical with a wire commanded detonation. There were rumors of laser commanded detonators, but I doubt it happened enough to warrant any sort of countermeasures.