Ask HN: What is a good way to track movement indoors?

I'm looking to track the movement of people in an indoor office building (with their permission) over an extended period of time. I would like to know who is meeting whom, at what times, how often etc -- the basic idea is to visualize physical interaction.

My thought was to use cellphone signatures, mac addresses etc to make this happen. Can anyone think of a good solution? Do I have to build something myself or is there something out there?