What?A Webcam for the front door. Otherwise known as a PostieCamTM
Why?A certain dissatisfaction caused by finding that the police don't have the resources to deal with burglaries. Twice.
How?From a software point of view, this was as simple as installing Motion. This is really quite a neat little package; it does motion detection, video capture and compression as well as a few other nifty things.
The hardware side of things is not that much more complicated. The software runs on the main household server, which has a Hauppage TV-capture card installed. The composite video input of this card is fed (via a long run of Cat-5) round the outside of the house to a tiny video camera, installed just next to the front door. This gets a good view of the driveway, and part of the pavement. The section of the pavement and road in the frame is masked from triggering motion detection, so that we don't infringe anyone's privacy (and also because we don't care if someone just walks past!).
Video files are stored on the server, and accessible over the Web. The system hasn't caught any burglars yet, but it does make it easier to find where the postman has hidden any parcels!