An investigation into why a Naperville police officer's Taser was fired inside the department's locker room is focusing on a possible equipment malfunction, Chief David Dial said Monday.

Dial said no one was injured when the Taser was discharged at 6:45 a.m. Wednesday.

He said the device made an unusual sound during the officer's routine spark check to ensure the equipment was working before heading out on patrol.

"I want to be clear that the officer was doing exactly what he was supposed to be doing by checking his equipment," Dial said. "The Taser made an unusual hissing sound before the officer touched the trigger and it discharged."

In rare cases, radio waves from an officer's hand-held radio have been known to cause such a malfunction, Dial said, but the officer did not have his radio on.

Cmdr. Mike Anders said it would not be unusual for a Taser to be in the locker room.

"Typically, we carry our weapons everywhere when we're on duty," he said. "Officers have received training as to proper testing procedures for the Taser."

Several area departments, including Aurora, Wood Dale, Oak Brook and Elmhurst, use Tasers to deal with a variety of incidents, such as fending off attacks, people who may be armed and threatening violence or suicide, those who choose to actively resist arrest and other calls with an elevated level or risk of danger to police officers.

The x-26 model used by Naperville and several other departments uses propelled wires to stimulate nerves in the sensory and motor nervous systems to incapacitate offenders. The model delivers 1,200 volts of electricity across a person's body. Its average current is one/21,000th of an amp, which is lower than the average Christmas tree bulb.