A college student has apologized for causing a scare on a New York city subway train when his science project short-circuited and started smoking in his backpack.

Gregory Kats, 29, says the device was just a model of an elevator’s inner workings. But it frightened riders on a B train near the Seventh Avenue stop on Thursday. Kats says he tried to reassure his fellow passengers that it was a school project — not a bomb — but people scrambled for the exits nonetheless. The box he was holding had a small battery, wires and a motor.

Kats, who was questioned by police and later released, says next time he’ll be much more careful and keep his electronic projects at home.

-with a report from CP