So the switch has one "normally open (NO)" and one "normally closed (NC)" contact. When the switch is "OFF" or in its normal state (normally pointed to the top left), you will get no connectivity through the NO side, and you will get connectivity through the NC side. When you switch it "ON" (normally pointed to the top right) that swaps - the NO terminals close and the NC terminals open.
If I'm reading P-J's diagram right, you only will get an alarm if your switch is CLOSED. So, you decide. If you want it to point to the top left to have the alarm be activated, you use the NC terminals. If you want it to point to the top right to have the alarm be activated, you use the NC terminals. How you wire it is not important as long as you understand that the alarm will only work when the switch is closed, and depending on which terminal set you use on the back will determin when it's closed and when it's open.