Think Google Analytics but for real life... I built an application for the Internet of Customers that monitors the demographics of visitors to your conference booth.
Active Demographic Monitoring: I used a Raspberry Pi with an HD camera that is set to take a photo every few seconds. The Pi has an OpenBR program running on it that checks whether or not a face was detected. If one is detected, it is POSTed to a Linux server that runs an OpenCV program to attempt recognition. The face can be recognized as a known SFDC contact. Regardless, estimation is attempted on age and gender and the mobile apps are updated in real time w/ average demographics.
BLE Beacons I used bluetooth low power beacons (Qualcomm Gimbal $10) and hid them in some Dreamforce badges. The beacons give off a bluetooth signal that the iOS apps can detect. Each of my SFDC Contacts have a beacon associated with their contact ID. When they approach the booth, the app detects which Contact is approaching and alerts the booth staff member.
iOS App Universal application. iPhone version is used to configure the beacon mapping to SFDC Contacts. The iPad has a demographic dashboard that shows age and gender distribution of your visitors as well as the list and faces of Contacts within range.