Audience response (or polling) systems are one type of technology you may have come across. At UEL some schools use TurningPoint which is an extension to PowerPoint enabling you to pose questions to your audience who respond via clickers.
Virtual polling systems provide an often preferable alternative as they avoid the need for special equipment such as the TP clickers above. One such example is polleverywhere.com which is free for up to 40 participants and accepts responses via txt, twitter or web therefore enabling the audience to use anything from a basic mobile to fully functioning laptop.
Other variants on this theme include txting to a number provided by the lecturer (see Ian Well’s example) or via a system like Txttools (now called Blackboard ConnectTxt) which we are currently considering as an add on to Moodle.
As more and more students turn up to class with smartphones, ipads and similar devices the opportunities for interaction increase.