A suitcase-sized NASA radar instrument, that can detect heartbeats, is helping disaster relief workers save lives of people trapped under rubble after a 7.1 magnitude earthquake shook Mexico City last week.

The technology called Finding Individuals for Disaster and Emergency Response (FINDER) was developed by NASA’s Jet Propulsion Laboratory (JPL) and the Department of Homeland Security’s Science and Technology Directorate in the US.

“Our hearts go out to the people of Mexico. We are glad to know our technology is being used to make a difference there,” said Neil Chamberlain, task manager for FINDER at JPL.

FINDER sends a low-powered microwave signal—about one-thousandth of a cell phone’s output—through rubble. It looks for changes in the reflections of those signals coming back from tiny motions caused by victims’ breathing and heartbeats.

In tests, FINDER has detected heartbeats through 30 feet of rubble or 20 feet of solid concrete.

It was also used in Puerto Rico last week to search for survivors of Hurricane Maria. While radar can not search through water, it is useful for detecting heartbeats through rooftops. People trapped in flooded buildings often run to the upper floors.

The technology evolved from JPL’s efforts to develop low-cost, small spacecraft radios, using signal processing developed to measure small changes in spacecraft motion.

FINDER is used alongside a variety of other techniques, including trained dogs, acoustic sensing devices and thermal imagers. All these techniques are usually deployed together.

When FINDER was deployed to Nepal after a major earthquake in 2015, it helped find four men trapped under a collapsed textile factory.