At the University of Texas Dallas, a researcher has developed a sensor the size of a button that could be incorporated into a number of form factors. The breakthrough which allows for the small size is a power optimization system that deactivates sensors when they're not needed. So when the system detects that the wearer is sitting, it stops monitoring them as closely as if they were walking or standing.
An Australian company, iStoppFalls, is working on a necklace-worn inertia sensor, called a Senior Mobility Monitor. But the company will combine the sensor with a training system, designed to build up seniors' reflexes so if they do fall, they do so in the safest way possible. (AARP recommends this method as well.) iStoppFalls' program takes the form of an Xbox/Kinect game, meant to be played thrice a week.