Reflecting back on 2011, there's one iOS app that I use several times a day. (Not counting the built-in apps, like Mail.) It's the mobile version of Sciral Consistency. I've written about the desktop version, and now the iOS version has completely supplanted my use of that, and increased its benefit by many times. Highly recommended.
Smarthome's tutorial for this is quite good. Basically you use a water sensor to signal your hem automation system when the tree is dry. As the tutorial says, you can get a message on your iPhone, or simply have the tree blink its lights. Setting it up so that it blinks S-O-S would be a nice touch.
Although uncredited, I consulted on this Popular Science technology roundup about wireless devices that monitor your home. Check it out in the October 2011 issue.
Also see this previous post.