To fight against cheating, China used a six-propeller drone during the college entrance exam in the country, AP reported.

Common methods used in cheating for China's exam include selling supposed answers, hiring surrogate test-takers and using wireless equipment to communicate during the test.

The drone scanned for any unusual signals that would manifest cheating as it flew over two testing centers in Luoyang city in central China's Henan province. On the first day of the exam, no signals were detected.

According to Huffington Post, Lan Zhigang, from Luoyang's Radio Supervision and Regulation Bureau said that the drone costs around hundreds of thousands of yuan, or equivalent to tens of thousands of dollars. It would be as big as a gas station pump when it is extended.

"A drone has its advantages. In an urban area full of tall buildings, various barriers limit the operating range of devices on ground, while the drone can rise up to 500 meters (1,640 feet) and detect signals over the whole city," Zhigang said. 

More than 9 million students took the exam that started on Sunday. Chinese high school graduates need to take the test to determine which university they are qualified to attend.

The exams take place for two or three days. After months of preparation, students travel to testing centers with their parents. Failure to pass the exam will allow them to repeat for another year or they could find a low-paying, blue-collar job, The Guardian reported.

According to the Education Ministry, at least 23 students had been arrested since late May because of cheating and would be barred from taking the test for up to three years.