If shouting across the office is not allowed in your place of work then a USB magic wand could be perfect for you. It connects to your PC with a USB cable which powers the device. You type the message on your PC which is then sent to the wand. You then wave the wand around and by using POV it displays the message in the air for all to see. Perfect 
Just dont go sending any secret messages that you do not want others to read.
Product Page Via: TechChee