Which version of Lionel 153IR do you have? For the exact same model number, Lionel has different instructions depending on which version you have (2015 or 2002). 
Hooking up the gate and speaker would be like the example shown at bottom of diagram.
Download/read instructions from Lionel site for whichever version you have (both manuals are on their site). There are 2 adjustment controls. You can wave your hand in front of the sensor window to trigger it to learn how the controls affect operation.
