The feds spent Tuesday in search of would-be suicide bombers at Penn Station.

The Transportation Security Administration began testing a heat-sensor camera — designed to scan large crowds for suicide-bomb vests — on the Amtrak concourse.

The SPO-NX equipment can sense heat emissions made by the human body — and tell when that heat is blocked by something such as a bomb vest or other dangerous gear under the clothes, according to manufacturer QinetiQ.

Amtrak cops, who are training on the equipment, scanned people in the crowd with the technology. A video on a laptop shows different colors for each range of temperature, and if a person’s torso is cooler than it is supposed to be, the screen alerts investigators.

Sen. Chuck Schumer (D-NY) had pushed for the TSA to bring the technology to New York after would-be suicide bomber Akayed Ullah detonated a homemade explosive in a tunnel leading to the Port Authority Bus Terminal in December, injuring himself and three people.

The TSA is testing in various cities to try to perfect the technology before it is installed permanently, said a source. The feds will be back at Penn Station Wednesday, the source said.