What is this?
 

I bought a truck and on the dashboard there is this little fob attached.. No idea what it does. Any ideas?

Re: What is this?
 

my guess is that it's an infra red receiver for something (most likely an aftermarket head unit or a digital TV box). If you have a device that uses a remote control, but want to keep the device out of eyesight, you use an infra red receiver as an extension so that you don't need to point the remote control at it every time.
Either that or it's a GPS antenna for a SatNav.