I created a door alarm using my Arduino, and it works fine. It beeps a piezo when a door is opened. It also hits a local webserver with the door pin that was opened (which sends an email).
The problem is that after a number of hours, it stops hitting the webserver and thus emails don't go out. It still makes the sound (and blinks a LED) so I know it isn't hanging or anything, and since it takes so darn long to stop working it is hard to debug. I just know that the next day it isn't sending emails anymore. I can hit the reset button or power cycle it and it will work fine. Any ideas?
Here's my original project: http://forum.sparkfun.com/viewtopic.php?t=12609&highlight=
Posts on my blog about the project (with code): http://www.russdraper.com/index.asp?search_for=arduino&page=blog&button=Search