A circuit tester is a simple tool used to check the electrical connections in a circuit. It helps identify whether a circuit is complete and functioning properly. Circuit testers can come in various forms, including multimeters and non-contact voltage testers, each designed for specific testing needs. These devices are essential for electricians and DIY enthusiasts when troubleshooting electrical issues. By using a circuit tester, users can safely determine if wires are live or if there are any faults in the circuit, ensuring safety and efficiency in electrical work.