Most of us have experienced that annoying buzz interference that can occur during a phone conversation.  When your smartphone is placed in proximity of a landline phone it can cause interface that interrupts dialogue and distracts the participants.  Moving the two phones away from each other can help with the problem, but you have to remember to separate before starting each conversation.  The company Buzz Killers came up with an ingenious coaster device that can mute the interference caused by smartphones.  You simply place your phone on this razor thin card and the problem goes away.

I recently received one of these as a giveaway from a tradeshow and I use it regularly.  The company allows you to order custom-branded versions of the cards for distribution to your employees or customers.  It is the ideal tradeshow giveaway in my opinion, because it is something that everyone needs, but also has a very small footprint that increases the likelihood it will actually be carried home with you.