Cribbing has long been a problem in India and, for Sunday’s government exams involving 1.6 million students in Rajasthan state, police had permission to snap mobile internet access while the tests lasted.

But one group planned to get around this with devices hidden in the soles of their flip-flops that could receive ordinary calls which would be transmitted wirelessly to tiny receivers hidden in their ears.

The plan was for accomplices outside to call the hidden contraptions and dictate the correct answers to the exams, said Priti Chandra, a police official in the western city of Bikaner.

But the group of would-be teachers were arrested acting suspiciously outside the examination hall on the evening before the exams and the devices in their footwear were discovered.

“We were aware of the possibility of cheating but we thought it would be a question paper leak or someone would use the internet, which is why it was restricted in many cities,” Chandra told AFP.

“But this was a totally new modus operandi. (They) are getting so tech savvy.”

Investigations revealed that at least 25 students had bought these flip-flops from a gang for 600,000 rupees ($8,100) per pair.

The information was shared with several other districts in time for the exams and many centers asked the students to remove their footwear outside the examination hall.

“In one case we caught a student after the exam and had to take him to a doctor to identify and remove the Bluetooth device from his ear,” Chandra said.

Cheating is rife in India’s highly competitive government, university and even school examinations and authorities have struggled with ever-more sophisticated methods to help people pass.

These include professionals who earn a living impersonating others and taking exams in their place, to gangs stealing or illegally procuring exam papers and then selling them.