On Jul. 26, 1881, Alexander Graham Bell first used a metal detector in an attempt to locate a bullet lodged in the chest of American President James Garfield.

President Garfield was shot in the back by an assassin on Jul. 2 as he entered a train station in Washington, D.C. The president lingered, his condition teetering between improvement and decline, until he died on Sept. 19. During the course of the months-long ordeal, the famed inventor, Alexander Graham Bell, added a technological contribution to the desperate struggle to save the president.

Working with his assistant William Tainter and other inventors and experts, Bell assembled his rudimentary metal detector in a few days. Refining the detector so that it would have an increased range beyond more than an inch or two, Bell tested it by firing rounds first into a wooden board and then into animal carcasses. Lastly, he performed tests on Civil War veterans who still had bullets in them.

Bell’s first attempt to use his induction balance device to find the bullet immediately encountered problems. A new condenser, added to the instrument for the purpose of amplifying the electrical charge, was causing interference in the sound receiver. The first attempt at scanning Garfield’s body proved a failure as the static made it impossible to correctly hear if the device was detecting a metal signature.

Bell returned to the White House on Aug. 1. His search for the bullet was now hampered by the president’s physician, Dr. Willard Bliss, who was convinced that the bullet was located somewhere on the right side of Garfield’s torso, and refused to entertain any notions to the contrary.

As Bell moved the device across the president’s chest where Bliss had told him to scan, he found nothing. Bell suspected that the metal springs of the mattress of the bed Garfield was lying on may have interfered.

Bell’s device had worked, even if it was not clear at the time. Bell was not able to find the bullet with his metal detector because he was looking in the wrong place.