This blog entry provides a good overview of keypad technology and also provides links to some experts in this field.
"Keypads are audience response devices that look like little calculators or remote controls. They are used in group meetings or events to collect audience responses or opinions, allowing audience members to interact with presentations, give feedback, and become more engaged in large-group settings. Keypads are often used as an added element in large-group deliberation and dialogue events."(Gasdaska , 2010)
Source: RunHappy (2008)