Beijing will install anti-spy devices to combat cheating during the national postgraduate recruitment examination this weekend, according to the Beijing Education Examination Authority.

Telecommunication signal detectors will be used to identify wireless earphones that are as small as a grain of rice, the authority said.

Exam cheaters have been known to evade detection by placing earphones deep inside their ears to receive signals from cell phones, which transmit answers to test questions from sources outside the examination halls.

Signal receiver are on sale for as much as as 2,500 yuan (about 320 U.S. dollars).

Officials with the authority also confirmed all electronic equipment, such as mobile phones and MP3 players, are banned from examination rooms at 73 sites in Beijing.

Any examinee found with banned electronic devices will be considered to have violated test rules and will be severely punished, officials with the authority said, without specifying the nature of the punishment.

Over 90,000 people will take the two-day graduate recruitment exams in Beijing, which is one of the key examinations in China.

Nationwide, more than 1.28 million people will take the tests, but only about 25 percent of them will secure immediate employment.

A string of exam-cheating scandals, including test paper leaks and surrogate exam-takers, have plagued exams in China in recent years.

The Ministry of Education (MOE) has warned students against buying fake exam papers sold over the Internet or via e-mail and text message ahead of the postgraduate recruitment exam.