For private companies and government agencies trying to track peoples' movements, technology is making the task increasingly easy.
Facial recognition and analysis are becoming increasingly popular surveillance tools — the technology was rolled out in airports across the world this summer as a tool for verifying flyers' identity, and is widely used by police departments for tracking suspected criminals.
Privacy-minded activists and lawmakers are now hitting back at facial recognition. The technology has been banned for law-enforcement purposes across California, and a similar bill is being weighed in Massachusetts. Meanwhile, artists and researchers have begun to develop clothes designed to thwart algorithms that detect human faces.
But emerging technology presents alternate means of identifying and tracking humans beyond facial recognition. These methods, also driven by artificial intelligence, detect the presence of humans using devices ranging from lasers to WiFi networks.
The vast range of biometric data that technology can register makes regulation difficult. Meanwhile, some of the emerging surveillance technology is already being embraced by military powers like the US and China.
Here's a rundown of emerging technology that can detect humans and track their location.