If an entry sensor, for example a door or window, was left open prior to arming the alarm, you would see the entry sensor icon showing as open on the alarm panel.
If you selected the icon, you would see which specific sensor was open.
If you arm the alarm panel, this message would display, giving you the option to continue or cancel, effectively bypassing the sensor when if you select 'OK'.
If you do select 'OK' and bypass the sensor, you will also see this pop up notification on you cell phone.
Important note:
If a door or window is open and bypassed when the alarm is armed, and then later closed while the system remains armed, opening that same door or window again will trigger the alarm.