Acoustic Observatory -- Low-Cost I have built what I call an Atmospheric Acoustic Observatory. It could also be thought of as a high-resolution barometer. There's a write-up on it at http://www.comfortlight.com/baro.htm. It is simple in principle, and it cost only about $50 for the main components including a red laser diode and a front-surface mirror that I cut into two tiny parts. An observer can see pressure changes smaller than 1 ten-millionth of atmospheric pressure. It can "see" long-wave sounds that ordinarily can not be heard. Even with all the windows open in my house, it can sense when someone opens or closes a door, silently to the ear, elsewhere in the house. One of my goals with this Observatory is to "see" long-wavelength sounds of thunder such as might come from approaching storms too distant to otherwise hear with normal hearing. It responds to the low frequencies of a human voice and passing car traffic, and it goes crazy when helicopters fly by within a mile or so of it. I also want to see, and hope to see, "microbaroms" which might trail in the wakes of hurricanes that I hope will come up the east coast this fall. (I live near Washington, D.C.) Check out the Wikipedia article on microbaroms. Distant earthquakes, thousands of miles away, might also produce "atmospheric tsunamis" that might be detectable with this device. A highly sensitive and low-cost seismometer could be built using the same basic principle of reflected laser light to amplify small motions. See the schematic diagram at http://www.comfortlight.com/SO.jpg. It's been operating for a month now. The main mirror, or "first mirror" got dislodged several weeks ago when lightning hit about a thousand feet away. A military jet, several thousand feet over the house, also dislodged the mirror.