A system for testing an electrical circuit includes a handheld device, and first and second plug-in modules. The handheld device includes a first sensor that senses a current within the electrical circuit, and a second sensor that senses a voltage within the electrical circuit. The first plug-in device is connectable to a first outlet of the electrical circuit and configured to provide an identification number on the electrical circuit. The second plug-in device is connectable to a second outlet of the electrical circuit and configured to display the identification number of the first plug-in device. The handheld device receives the identification number from the first plug-in device and displays the identification number.