The sensor uses a directional infrared LED beamed at a sensor that shoots past where you'll walk. When you interrupt the light from the LED, the LEDs turn on for a period of time that you can adjust. There are a lot of advantages to using IR LEDs over lasers; they're safer to work with since lasers can damage your retina if you stare at them, they're a lot easier to aim since you're pointing them at a small sensor usually across a hallway, they use really low power, and of course they emit no visible light which makes them stealthy and therefore cooler. The biggest drawback? Sunlight or incandescent lights generate infrared light, so if you put them in an area where they get hit by this light they won't turn on. I actually feel that this is an advantage as well, since it keeps them off during the day when you don't need them.
Please note: this project is designed to assume that you have at least a basic knowledge of electronics, electronic schematics, and know how to handle and mount static sensitive devices. You need to know how to solder, and more importantly how to solder on tiny chip leads that can only handle a brief hit of heat before they fry and turn into slingshot ammo.
Play the high def video. I'm a terrible cameraman so sorry if it's shaky!