<p>Clickers vary. Some are over-glorified wireless mice (i.e. left/mouse click and mouse movement)</p>
<p>Some will emulate certain keys on the keyboard, e.g. cursor up/down, page up/down and perhaps a few other powerpoint type keys like "B" for blank.</p>
<p>Some more expensive ones are programmable and you can pretty much do what you want with them!</p>
<p>For operation with OpenLP v1.x at the very simplest you need something that will do Page Up and Page Down to change slides.</p>