How to make the Arduino have Game Controller Detection?

Hi. How would I go around making my Arduino UNO detect when something has been plugged in to the digital pins?

By that, I mean, I have a SEGA Controller wired up as seen here http://youtu.be/xB74yYl5894 but when nothing is plugged in, it beeps constantly, stops for a second, then starts buzzing again (as I added in a buzzer + LED).

How can I make it KNOW when a controller has been plugged in?

You are going to destroy that pin that has the LED with no resistor. It's only a matter of time.

Oh, I though pin 13 had a resistor on it? Better add one of those then...

Oh, I though pin 13 had a resistor on it?

No, the LED that is connected to pin 13 has a resistor. That resistor has nothing to do with limiting the amount of current that you are also sucking from the pin (more than the Arduino can safely provide, that is).

The LED is sucking the voltage it needs?

I thought the Arduino outputted the voltage (3 volts) on pin 13. Above that pin, is ground (GND).

The Arduino controls the voltage. The powered device pulls the amount of current it needs, assuming that the current can be supplied.

Voltage is pushed. Current is pulled.