Every once in a while the signal on my wifi drops below -80dB. I've got a directional antenna for my desktop computer so I can pick up my landlord's wifi, which is just at the edge of usable range. I bought a cheapass wifi extender when I first moved here, but the thing is so crap that it keeps crashing on heavy load, so I bought an antenna instead and now connect to the main wifi. I use inSSIDer to determine the optimal position of the very short antenna, but the strange thing is, that optimal position changes every other week or so. Eventually the signal strength drops from ~-79dB (very usable, about 2 megabyte/s) to -86dB (completely unusable, frequent disconnects, internet unbrowseable).
Why? Are my neighbours constantly moving things around, placing thick slabs of concrete between the router and my apartment? Or are they moving the router around? Or is it the weather? I wonder if, with some calculations based on signal strength of the wifi networks around you, you can detect roughly the position of moving objects based on the signal strength of each wifi network. A side project perhaps, if I weren't already working on 3 other side projects..