The Monitoring app has a number of 'off the self' security & safety sensors along with an energy monitor connected to an Impee. There is also a controller "lamp box" impee I used from another project.
Most of the solution is built on the e.imp platform for details e.imp I've a cloud server for storing time stamped sensor data & which also calls a set of web services I use the Pushover.net for alerts, this a fantastic service.
Update: I've now managed to combine several sensors into one "uber sensor" based on the imp. I've built a few of them for friends and family there more at socialsensing.co.uk
Alerting
Visual prompting
Hardware & Sensors
Architecture