Because the satellite signal is not strong enough to penetrate it sufficiently for the receiver to acquire it. It has problems with heavy foliage as well.
Some of the better GPS will pickup inside signals and there is a mention in one of the forum threads of a person who did get there GPS from Parallax to work inside by a window.
But Martin is right, getting a GPS signal inside is something you should consider non-existant.
Comments
-Martin
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StampPlot - GUI and Plotting, and XBee Wireless Adapters
Southern Illinois University Carbondale, Electronic Systems Technologies
But Martin is right, getting a GPS signal inside is something you should consider non-existant.