These devices are commonly referred to as “Clickers.” Each student in the class gets a small keypad which allows them to respond to questions posed by the instructor. Their responses are collected by software on the instructor’s computer and the data can be saved for later analysis. The student responses are also displayed as soon as the polling time has expired allowing the instructor to see if further discussion is required or if the class can move to a new topic.
You may be interested in reading the ELI 7 Things You Should Know About Clickers here.