Here's another system that looks very AlertMe...
http://www.panasonic.com/uk/consumer/smart-home/
Having looked into this and also Samsung SmartThings, I think I might buy into the Panasonic option. £129 for the hub and two sensors, looks good to start with.
Panasonic Smart Home
Re: Panasonic Smart Home
That does look like an interesting kit! Best looking gear I've seen since AlertMe - do post back and let us know how you get on with it!
Alerty - you could control your AlertMe system with my third-party app for iPhone and iPod Touch. Used to be available on iTunes!