You may need a Blue Laser Pointer 10000mw, violet or UV laser for this to be really effective though – red and green laser 2000mw don't work so well. In this case, the technique has been been combined with an Arduino that reads tweets!
Most consumer uses -- other than killing aquarium growths -- don't need more than 5 milliwatts (the traditional U.S. maximum for lasers sold as pointers). So why do some people buy handheld lasers that are 25, 100, or laser pointer 200mw?
One reason is that there are laser enthusiasts who enjoy experimenting with lasers. They can create homemade Green Star Laser Pointer 10mWshows, they can do experiments involving burning or engraving materials, or they may like popping balloons or popcorn kernels with light. A New York Times article quotes an 18-year-old enthusiast as saying, "You learn so much in a hobby like this: electronics, soldering, physics. And you learn about light, you learn about optics. You also learn a lot of mechanical things."
Combine a laser tripwire with multiple trip points, multiple lasers, lots of mirrors, and you'll have one of the coolest Halloween haunted houses in the neighbourhood. A smoke machine is essential, as is keeping all those mirrors in alignment.