Chinese scientists are developing a mini-camera to scan crowds for highly stressed individuals, offering law-enforcement officers a potential tool to spot would-be suicide bombers.
But the technology has raised concerns over its implications for individual privacy and potential abuse by government agencies.
Stress has a range of effects on the body. It can register as changes in heart rate, facial expression and body temperature, which scientists can already monitor from a distance. But the readings are not always reliable. For example, with enough practice, a person can learn to control their heartbeat.
That's why Chen Tong , an associate professor of electronic information engineering at Southwest University in Chongqing looked at another indicator - the level of blood oxygenation. Using hyperspectral imaging, which examines information across the electromagnetic spectrum, Chen and his research team have developed a "stress sensor" that measures the amount of oxygen in blood across exposed areas of a body, such as the face. "The higher the mental stress, the higher the blood oxygenation," he said.
Chen's research comes amid heightened fears over security on the mainland after a series of deadly attacks in public places. According to the authorities, the assailants ranged from knife-wielding religious extremists going on rampages in train stations to distraught citizens setting fire to crowded buses.
"They all looked and behaved as ordinary people but their level of mental stress must have been extremely high before they launched their attacks. Our technology can detect such people, so law enforcement officers can take precautions and prevent these tragedies," Chen said.
Officers looking through the device at a crowd would see a mental "stress bar" above each person's head, and the suspects highlighted with a red face.
The researchers said they were able to use the technology to tell the difference between high-blood oxygen levels produced by stress rather than just physical exertion.
Laboratory tests of the technology had yielded encouraging results, he said. But getting the device to work in the field presented new engineering challenges. The biggest obstacle was acquiring the remote data.
For example, security officers deployed in a busy bus station would need to filter a tremendous amount of data and process it in a short amount of time. Such computing power is not available in smartphone-sized devices, so officers would need to send the information to analysts off-site, over a Wi-fi network, which introduces a new set of challenges.
Chen said Professor Liu Guangyuan, at the same university, had also been working on a wrist strap which officers would "cuff" onto a suspect to measure heart rate, galvanic skin response and breathing rate. "The suspected terrorists could hopefully be filtered out by non-contact devices and then be checked more intensively with contact devices," Chen said.
But Li Jiancheng, a resident in Shanghai's Pudong district, said he worried the technology would be abused by the authorities. "The technology can be used on terrorists, but harmless people such as petitioners and protesters could be the target as well. I would feel uncomfortable and tense if a police officer stared at me through strange goggles," he said.
Chen said they would not let their technology out of the lab for commercial use until there were laws to regulate its use.