A big part of home automation is finding sensors that can feed your smart home the information it needs to make decisions for you. Hobbyist automators are known for concocting all sorts of Rube Goldberg style methods for knowing when a car enters the driveway, for example.
That's why Dylan Field's post Radar Roundup: Sensors - O'Reilly Radar caught my eye. Field discusses several different types of sensor applications that are more broadly being used across the web, and might inspire you to adapt them for home life, too.