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A new technology allows public surveillance cameras to send personalized messages to people without knowing the address of the phone. The technology can be used by governments to enhance public safety, for example, deploying cameras in high-crime or high-accident areas to warn specific users about potential threats, such as suspicious followers. This dual-use development can also provide tailored information to visitors at museums or historical sites.

Developed by researchers at Purdue University, PHADE digitally associates people in the camera’s view with their smartphones by using the subjects’ behavioral address, or the identifiers extracted from their movements in the video.

While traditional communications require an IP address or a media access control (MAC) address to deliver messages to the right device, PHADE employs a unique method of matching messages to recipients. A video stream tracks the movements of people within range, then analyzes and encodes those movements as an “address.” At the same time, an application on a subject’s smartphone is doing the same analysis using the phone’s sensors.  When PHADE broadcasts a message it will be received only by the smartphone that has a matching “address.”

After encoding a user’s movements to create an address, PHADE “blurs” the data to prevent it from being used to identify the person. Plus, it allows the personal sensing data to remain on subjects’ phones instead of asking them to upload the data to server.

Still, there’s something unsettling about a communications system that watches our movements and sends messages based on what we are doing. Yes, it may save us from being run over by an approaching car, but it may also pester us with advertisements as we walk through a store, according to

As He Wang, assistant professor of computer science said, PHADE does not violate the privacy of smartphone owners. It does nothing to identify the users or anything about them other than how they move.  But PHADE does offer a unique opportunity for government or companies that license the technology to intrude on individuals.

How PHADE is used will depend on the types of applications licensees build and whether end-users allow those applications on their smartphones, Wang said. “We provide a way to communicate, but how to use it depends on the entities who apply our work.”