In a time where getting the components to make a “dirty bomb” in the U.S. can be frighteningly easy, a federal government agency used D.C. ambulances to advance the use of tools that sniff out radiological threats.

The Defense Advanced Research Projects Agency, which works to improve technologies for national security purposes, announced the completion of its biggest test deployment of detectors that help prevent attacks that involve dirty bombs and other nuclear weapons.

The devices can pick up everything from natural granite at construction sites to lingering radiation after medical treatments, but they are made to distinguish benign sources from threatening ones.

DARPA’s Sigma program began the deployment of its vehicle-mounted, nuclear and radiation detectors in July of last year, in partnership with D.C. Fire and EMS. Officials installed about 73 detectors on a fleet of ambulances over a seven-month period. As the vehicles whipped across the city, they logged over 100,000 hours of detector operation, which identified thousands of radiation sources in real time, before concluding in February.

In addition to this longer-term test that featured large detectors, DARPA has also overseen shorter tests, including a one-day experiment in October where people put smaller, smartphone-sized detectors inside of backpacks and walked around the National Mall for hours.

D.C.’s data will be used to help fine-tune Sigma’s system so officials can potentially deploy the detectors in other cities and so that active-duty military units and National Guard civil support teams can use them for emergencies, said Vincent Tang, DARPA program manager, in a release.