Several standard solutions have been developed for problems encountered when monitoring laboratory response sensors with microcomputers. These problems include voltage-level translation, power-supply isolation, contact debouncing, and temporary data storage. Data storage has typically been accomplished through the use of edge-sensitive devices, which introduce difficulties when a researcher wishes to monitor the duration of a response. A circuit is described that includes an optoisolator with a silicon-controlled rectifier at its output stage. The circuit acts as a latch for the detection of brief responses, and, because it is not edge-sensitive, it can also be used to record the duration of sustained responses.