Just before noon on April 25, 2015, the ground in Nepal started to move. For about 30 seconds, people felt the ground shaking beneath them. It doesn’t sound like a very long time, but it doesn’t take long for an earthquake to cause damage.

The ground shook so much and so hard that houses cracked, buildings flattened, and thousands of people were hurt or killed.

After the earthquake, cities and villages were ruined. Where there used to be buildings, there was now only broken pieces. People were trapped under collapsed houses. To save people, you had to dig them out. But first, you had to know where they were.

How can you find someone buried under rubble? You can’t yell their name because they won’t be able to hear you.

If they yell for help, you can’t hear them either. What you can do is listen for their heartbeats.

You might be thinking, ‘heartbeats are very quiet, you can’t just hear them’. That’s normally true. You can’t hear them with your ears, but you can find them with a special machine.

This new machine is called FINDER. That stands for “Finding Individuals for Disaster and Emergency Response”.

It uses radar to look for people under bricks, mud, and pieces of buildings. It was built by scientists and engineers from NASA and the United States Department of Homeland Security.

FINDER is the size of a suitcase. It weighs about as much as a two gallons of water.

When rescue workers need to find someone, they turn it on, and the machine searches for heartbeats. It can sense a heartbeat even if the person is buried under 30ft of broken concrete.

When the earthquake hit Nepal, the people who built FINDER knew it would be very helpful. They brought two of the machines to Nepal right away. On April 29, they found four men trapped under collapsed buildings. FINDER saved their lives.