If you plan on a vacation, here is a great project to track the temperature and soil moisture of your Plant using dweet.io and AWS IoT.
Radio emissions from sky sources like Sun and Jupiter can be received and converted to digital domain for processing.
Know when your clothes are dry
Air Quality Monitoring that uses the Intel Edison Compute Module, Amazon AWS, Visualization through Kibana, and drones!
This projects shows a simple environment monitor which sends you an EMail when an abnormal weather condition is detected.
It's a pretty common question, and all the solution takes is an Edison, AWS, wire and photoresistors.