At Carriots we have created this nice and very simple tutorial: How to connect an Arduino to Carriots and build an Alert System. https://www.carriots.com/tutorials/arduino_carriots/alert_system
This systems detects lights with a LDR sensor and send the information to Carriots where an Application is built to send you a warning via SMS.
This tutorial could be the first step to do a DIY home alert systems based on motion detectors or door openings sensors.
Carriots is FREE to use for up to 10 devices. The free account also let you sens SMS and emails!
Here is the project Schema of the project: