I have magnetic door sensors (so they're really just basic switches).  I'd like to know if there's a way I can connect these sensors to my Raspberry Pi's GIOPs and determine whether these sensors are allowing current through or not.  Can any of the GIOPs be utilized to directly interface with the switches?  I have a switch right now in a breadboard and would love to know if there are two pins on my Raspberry Pi that I can safely connect to the switch to play around with.  This might be a dumb question, but is a 1k resistor required to be in the circuit too?  

My Raspberry currently has WiringPi compiled and it's also got the ruby wrapper for it too, so I'm able to control the pins fine in S/W, I just don't know how to "sense" the pins safely without wrecking this device.