Do you know how much of your office space is underutilized? These sensors can tell you — or when your grandma takes a fall

Knowing where people are in a building at any moment is valuable information, and a variety of technologies now exist to make it easy to turn a home or office into its own tiny surveillance state.

Using video cameras or simple motion-tracking sensors, these technologies can tell when unneeded energy is being used in empty rooms and where companies are wasting leasable square footage on vacant desks. And in the context of senior care, they can even save lives by alerting health workers if someone has fallen or is unresponsive.