A housekeeper in Tempe, Arizona, was cleaning the room of 18-year-old high school senior Joshua Prater when she stumbled upon an improvised explosive device.

The unnamed woman was unaware that the device posed an immediate threat to her life, so she drove it to a nearby fire station herself.

There, firefighters contacted the Tempe Police bomb squad, which sent over investigators to examine the device.

"They had it X-rayed, they saw it was a valid IED," Tempe Police Sgt. Mike Pooley said. "It was something that wasn't big, but could cause serious injuries and the death of someone."

Pooley said the device was "ready to go" and just needed a trigger.

Prater was subsequently arrested on charges of misconduct involving weapons and possessing a prohibited weapon.

He reportedly told police that he constructed the device eight years ago and was unaware that it still contained explosive powder.

However, upon searching Prater's room, police uncovered additional bomb-making materials.

The purpose of the device remains unclear.

Pooley commended the cleaning lady on her quick action, saying that although she risked her life to deliver the device to the authorities, she ultimately "did the right thing."

[mug shot via AZFamily]