Displays the status of light on the smart phone app.
Area Intrusion Monitor A PIR sensor monitors a room and sets off audio alarm / email notification when it senses a moving body.
Garage Door Monitor This is handy if you can't see your garage door from the house.
I'm more focused on extensive networked sensors, timely alerts, and aesthetically appealing presentation of events. With Arduino, it's really easy to connect boatloads of cheap sensors.
Using this setup, that boatload of cheap sensors can now be on the internets.
Temperature / Humidity Sensor Temperature and humidity is reported to the mobile app.
Optionally, you can enable email notifications when temperature dips below/above some preset value.