He put a camera in his boot to take 'upskirt' photos. Then it exploded.

A spy camera concealed in a shoe. A Wisconsin man is being questioned by police after his device's battery exploded. Photo / supplied

Wisconsin police are questioning a man over a suspicious shoe fire that caused him to seek medical attention.

The 32-year-old had installed a camera in one of his shoes so it could peer up and take illicit photographs of under women's skirts.

But Madison police said things went wrong before he could engage in the illegal activity.

He was testing the camera's functionality at home when the device's battery exploded, subjecting his toes to minor burns.

"When the explosion happened, he got treatment for minor burns, then disclosed what happened to his mentor, a clergyman," officer David Dexheimer told the Wisconsin State Journal.

Madison Police Chief Mike Koval said the man, in the company of his priest, surrendered himself to police for a 'sex offence'.

"The subject reported he had purchased a shoe camera that he intended to use to take 'upskirt' videos of females, but the camera battery had exploded prior to obtaining any video, injuring the subject's foot," Koval says.

He was "counselled on his actions and released from the scene as no illicit video had been taken. Investigation continuing."

Wisconsin state law considers it an offence to knowingly install devices for the practice of 'upskirting', the State Journal reports. The act is an offence in some US states, but not all. Wisconsin recognised it as a felony in 2015. Offenders face a three-years and six-month jail term and a $NZD14,770 fine.