I got an oddball idea for an app, but, as I can't really test it at my current location, I won't make it. So, I thought I'd post it here, in the hope that someone else might get inspired and do it. Then, I thought a little bit more, and realized that there are many good ideas that never get made, so I expanded it into a "Post your idea that you'll never make, and maybe someone else can use it" thread. So, here's my idea, feel free to use it: Aurora detector We've recently had some splendid aurora borealis (also known as northern lights) here in Sweden. As usual, though, I missed them. I've missed many auroras, and have never actually seen one live, and I really would like to see them. So, I started googling for how to build an aurora detector, and found that it wasn't that difficult. Basically, it looks for fluctuations in the earth magentic field using a compass of some kind ( http://aurorawatch.lancs.ac.uk/detectors/ ). By now, you probably see where I'm going. Our phones have a magnetic compass inside them. Moreover, they usually just lie still at night, beside the bed. So, if one made an app that waited until the accelerometer showed the phone at rest during the dark hours (the auroras won't be visible during daytime anyway), then checked for fluctuations of the magnetic compass, one could detect auroras (or, possible, cars moving nearby...) and raise an alarm. Sounds very doable, if you ask me. My problem is that I live in central Sweden, where we have auroras maybe once every few years. Testing is next to impossible (especially as I tend to miss them...). So, maybe someone who lives far north or far south will pick up this idea? Anyone else with good ideas you won't do, but hope will interest someone else?