This systems detects lights and send the information to Carriots where an Application is built to send you a warning via SMS. This tuturial 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!
For less than 75$ in HW you can have your own Home Security System with no montly costs!