Risco RWX780868M3C WiComm Pro Wireless Slim Door ContactWe usually fit these on your front door, or your main entry exit door. If you have a porch we would usually install this on the main front door to your house. If you would like to use multiple entry exit routes then you will need one of these for each door. We would recommend that you have a door window contact fitted on any external doors that you want to enter or exit via when setting or unsetting the alarm system as this triggers the entry exit