A bone-conduction earphone the size of a grain of rice may have been used to cheat on the TOEIC English proficiency test in Japan, police sources said Tuesday.

The earphone was confiscated from a suspected test cheater, along with a pendant-shaped relay device and a roughly 40-minute video explaining how to use the equipment, according to the sources.

The suspected cheater was one of 10 Chinese test takers at the same test venue as Wang Likun, a 27-year-old graduate student at Kyoto University who has been arrested in the case.

The earphone, which was several millimeters in size, was designed to be removed from the ear using a magnetic stick. The relay device was for connecting to a smartphone.

The international crimes division of Tokyo's Metropolitan Police Department believes that the equipment was provided by a Chinese business offering cheating services.

The video explained in Chinese-language audio and subtitles how to use the relay device, including linking it to smartphones via Bluetooth.

In May, Wang was arrested at the test venue. He had a small microphone about 3 to 4 centimeters long hidden in his mask.

Wang has been served another arrest warrant for allegedly impersonating another person to take a TOEIC test in Tokyo's Nerima Ward on March 1. Fourteen Chinese nationals applied for the same day's TOEIC test using the same address in Tokyo's Nakano Ward as Wang.