My wireless door and window sensor does not indicate a correct open or close status at the keypad. How can I fix this?

First, open the door or window where the new sensor has been installed, and wait for 2 seconds before closing it. Now you can arm the system.

Similarly if that door or window is already open, then close it and wait for 2 seconds or more before arming the system. This will allow the keypad to register the correct status of that sensor and thereafter during ongoing operation.