Continuity testers check the continuity on wire, fuses, circuit breakers and other electrical systems. They detect if the circuit is open and something is blocking the electricity's path. Continuity testers typically consist of a battery in a housing with a test probe at one end and a test wire and alligator clip at the other end. Once the electrical system is de-energized, the alligator clip is secured to one wire or connection. When the test probe touches a separate wire or connection in the system, the continuity tester's battery sends electricity through the tester and system to complete an electrical circuit. The continuity tester either illuminates or buzzes to indicate a closed circuit. If the circuit is open and electricity cannot make it back to the tester, no indicator goes off.