I was doing a quick bit of Googling and bumped into a couple of interesting pages; one from David Boyce Design and the other from eg technology.
Those links take you to design concepts for the AlertMe devices. They're the more recent variant of the motion sensor, plus a version of the alarm sensor that hasn't been brought to market. I believe the button design is also revised from the version that can be purchased too, as there was a move a year or so ago to make the devices a little easier to open and change batteries. The design change with the removable back also made it much more straightforward to screw the devices to a wall (instead of using the weird stretchy adhesive).
Taking a look at other brands of wireless home security devices, it's clear that the AlertMe kit is still way ahead. So many of the competitors have ridiculously huge and ugly PIR sensors.
Design of the AlertMe System
Design of the AlertMe System
Alerty - you could control your AlertMe system with my third-party app for iPhone and iPod Touch. Used to be available on iTunes!