Police are calling a contraption believed to be an explosive device found at a Phoenix high school a "convincing hoax," FOX News has learned.

Phoenix Officer James Holmes said a female student at Washington High School spotted two cylinders with wires and a clock attached tied to a light pole in the school courtyard.

The girl told teachers, who thought it was a bomb. Police called to the scene investigated and determined it was a fake — but a convincing one, according to Holmes.

Students were evacuated and transferred to the football field after police received the bomb-threat call.

Reports of a gunman in the premises also turned out to be false.

A bomb-detecting robot squirted water at the makeshift device, and a squad retrieving it from the scene determined it was a bomb "look-alike," Holmes said.

The school's automatic "outdial" system called 1,600 parents Thursday morning to alert them of the situation.

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