Troubleshooting Arduino Notifying Doorbell

I'm not very experienced in electronics and I'm trying my hands on this project: http://makezine.com/projects/notifying-doorbell-with-pushingbox/. I did everything correctly and I think I even have the same doorbell. I also decided to do all the other steps first and then step 3. The problem is that whenever I connect the wires to the doorbell buttons it rings continuously. I think the current from the Arduino is closing the circuit. How to fix this? Thanks

Check polarity on the doorbell button. I guess u measure a voltage.. Connect negativ to arduino GND and the other to a pin (2 or 3.. the guide is misleading) Define this pin INPUT.