by Dimitris Platis @ instructables.com:
During presentations, I avoid being stationary and generally like to walk around in order to increase the interaction between me and the audience. However, I am constantly being faced with the burden of having to go back to the laptop, in order to change a slide or tell a person sitting by the laptop to do that. Not cool!
This problem is usually solved by devices, called remote clickers or wireless presenters, which consist of a handheld controller with buttons that sends signals to a USB dongle plugged in the computer. After looking around to buy one, I could not find any decent option costing less than 10$. So why not make one?
Simple, easy and cheap wireless presenter – [Link]