The only way I can think of that a false alarm could occur is if a light within the camera view burns out, or there's a power outage that causes the lights to go out, even for a split second. In both cases, the PC camera would instantly detect the sudden difference in lighting and would trigger. The PC is not affected by a power outage because it's hooked up to an uninterrupted power supply.  Three clues could tip you off to a possible false alarm.  

1. There would likely be only one or two images present. If someone walks through the camera view, it normally generates at least 4 images.  Prior to us leaving on December 24, I put some sample images out there for the GPD to look at.  However, before I leave, I'll clean them all out, so there should be no images present. 
2. The image(s) would be dark, then bright or vice-versa.  Normally the lighting is the same between them.
3. There would be no person in any of the images.

If you see a person in any of the pictures, it's almost 100% certain that a real burglary is in progress.  To understand why we can be so sure, you need to understand how the GOTCHA! software alerts us.

1. When the GOTCHA! software detects a change in the camera image, it instantly starts uploading images to this web site at the rate of about 1per second.  Since it uses a RoadRunner connection, it's very high speed.  It would be next to impossible for someone to prevent at least 2-3 images from being uploaded before turning the PC off because they upload so fast.
2. At the same time it's uploading the images, it's also using the PC's modem to send a numeric page to our pager.  We have nationwide access with our pager, so we can be reached almost anywhere.  We normally get the page within 30-60 seconds of the person stepping into the field of view of the camera.  If we trigger it ourselves when we come home, we'll just ignore the page.  Otherwise, nobody should be in the house while we're gone, so it will likely be a real burglary if we call you.
3. I have found from my tests that each time they walk through the field of view they trigger a new page to our pager. So two or more pages would be a strong indication of a real burglary unless it was one of the two false alarm situations described above.