Circuit testers, also known as circuit testers pens or test lights, are handheld electrical testing devices used to check the presence of electrical voltage and test circuit connections. They are commonly used by electricians, technicians, and DIY enthusiasts for troubleshooting electrical circuits and identifying faults. Here are some key features and functionalities of circuit testers:

1. Voltage Detection: Circuit testers are primarily used to detect the presence of voltage in electrical circuits. They can determine if a circuit is energized or de-energized, helping to ensure safety during electrical work.

2. Non-Contact Operation: Some circuit testers feature non-contact voltage detection, allowing users to detect voltage without making direct contact with live wires. They use proximity or electromagnetic field sensing to detect voltage, making them safer and more convenient to use.

3. Visual and Audible Indication: Circuit testers typically provide visual and audible indications to alert the user of voltage presence. They may have LED lights that illuminate or change color, or they may emit beeping sounds to indicate voltage.

4. Continuity Testing: Circuit testers often include continuity testing capabilities, allowing users to check if a circuit is complete or if there is a break in the connection. This is useful for checking for open or short circuits and verifying proper wiring connections.

5. Polarity Testing: Some circuit testers can determine the polarity of a circuit, indicating the positive and negative terminals or connections. This is especially useful when working with components or devices that require correct polarity for proper operation.

6. Battery-Powered: Circuit testers are typically powered by batteries, making them portable and easy to use in various locations. It is important to ensure the batteries are properly installed and have sufficient power for accurate testing.

7. Safety Features: Circuit testers often have safety features to enhance user safety. These may include insulated probe tips, shock-resistant casings, and built-in self-test functions to ensure the device is functioning correctly.

Circuit testers are versatile tools for quickly and safely testing electrical circuits and connections. They are particularly useful for basic electrical testing, troubleshooting, and identifying faulty wiring or components. However, it is important to note that circuit testers are not designed for detailed voltage measurements or comprehensive electrical testing. For more advanced testing and accurate voltage measurements, other instruments such as multimeters or oscilloscopes should be used.