Continuity testers are electrical test instruments that are used to determine if an electrical circuit exists between two points. They consist of an indicator that is connected in series with a power source (usually a battery), and two test leads or probes. The indicator is activated if the probes detect a complete circuit between the leads. Some continuity testers have visual indicators such as light emitting diodes (LEDs). Others feature audible buzzers. For high-resistance circuits and applications which involve sensitive electronic components, low-voltage and low-current continuity testers should be used. Typically, these devices contain an operational amplifier or op-amp.  

Output interface is an important specification to consider when selecting continuity testers. Choices include binary coded decimal (BCD), digital-to-analog (D/A), universal serial bus (USB), general-purpose interface bus (GPIB), and RS-232. Selecting continuity testers also requires an analysis of options such as battery power, overload protection, and alarm types. Battery-powered devices are lightweight, portable, and suitable for in-field use. Continuity testers with overload protection have fuses to protect internal circuitry from voltage spikes. Products with visible alarms light up when the root mean square (RMS) value or peak value is greater than a given range.   

There are many different form factors for continuity testers. Benchtop units are designed to sit atop a bench, often in a laboratory setting. Free-standing devices have a full case, cabinet, or integral interface. Clamp meters are continuity testers that measure current through wires that are still connected to the circuit. Rack-mounted devices come with hardware such as rail guides, flanges and tabs and are designed to be mounted in computer or telecommunications racks. Handheld continuity testers are designed for operation while held in one hand. Continuity testers with a computer-board form factor are printed circuit boards (PCBs) that plug into computer motherboards or backplanes. Electrical test equipment with other form factors is also available. 

Many continuity testers bear quality marks and comply with recognized standards for performance and safety. CE Marking indicates that a continuity tester complies with the essential requirements of relevant European Union (EU) directives that uphold national standards for health, safety, and environmental protection. Continuity testers that bear a CSA Mark have been tested by the Canadian Standards Association (CSA) and meet applicable standards from organizations such as Underwriters Laboratories (UL). Recognized standards for safety and performance include the EU’s Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronics Equipment (WEEE) directives. IEC 61010 from the International Electrotechnical Commission (IEC) is another important standard.