At technical colleges and secondary-level tech schools, students enrolled in basic electronics labs who have learned about diodes that do rectification are used to seeing power diodes like the 1N4001. When the students are introduced to low-power zener diodes and signal diodes, component identification gets more complex. If the small zeners are inadvertently mixed with tiny signal diodes, distinguishing one diode type from another can be difficult. A student or an instructor can quickly discern a zener diode from a signal diode by using a diode checker. The zener's operating voltage can be determined as well. Identifying a lesson's required diode type by using a diode checker will allow a student to more accurately assemble his or her lab assignment--and help the student acquire more technical knowledge and lab skills. This article discusses how a diode checker works. This article also describes how to build, set up, test and use a diode checker. (Contains 3 photos and 5 figures.)