push-button switch on robot

[Conan]

Hello, for autonomous mode, we were thinking about putting a momentary push-button switch on the front of the robot so we would know if we hit an obstacle (wall, robot, etc.). So, I went down to Radio Shack and picked up a button. The button (like most switches) has two leads that are connected when the button is pushed. How would be attach this to the robot controller? Doesn't the controller have three leads (power, signal, ground)? Thanks.