If you have a recent MacBook or MacBook Pro, chances are good that you have a built-in seismograph — an instrument that measures shaking. These are the things that are used to measure earthquakes.
What you have in your laptop is actually a Sudden Motion Sensor. This is a cute little device that tries to determine if your laptop has been dropped or otherwise jolted. If so, it parks the hard drive, hopefully preventing damage. That’s pretty cool on it’s own, but what’s even cooler is that there’s a way for applications to read the sensor and use it’s data.
Enter SeisMac and iSeismograph. Both programs display, in real time, the data from the Sudden Motion Sensor. The chip measures the acceleration in all three dimensions. In particular that means the vertical axis will always report 1 “g” of acceleration, as long as the computer is level. If you’re like me, that’s a dangerous thing to know, because you will then be tempted to find out if your laptop can achieve free-fall. (It turns out the answer is “yes”.) With iSeismograph (which seems to be the one with a lot more bells and whistles) you can also make a 2 dimentional plot of, say, the X axis versus the Y axis, and then try to use it as an Etch a Scetch.
Is this useful? Possibly. There’s an idea to use this to report seismic events to get better resolution earthquake data, SETI@HOME-style. Each computer would report seismic events to a central database, where detailed analysis could be done. The Quake-Catcher Network is actually doing this. They’ve made some good progress solving the obvious problems of how to determine the computers location, and how to tell an earthquake apart from a cat. The press release for iSeismograph also mentions a number of other good educational applications.
Mainly, though, it’s just really cool.