Each sensor can be in one of 6 modes: disarmed, armed - away, armed - at home, sleeping, entertaining and extended away. When you set the house mode using the security panel, all sensors in the house are by default set to that mode. It is possible to arm zones separately, however, that is an advanced setting.
On this page you indicate which sensors are active when in the indicated mode. Note that you are not specifying HOW LinuxMCE will respond to the sensor. That is done elsewhere. On the Wizard/Event Handler/Respond to Events page you tell LinuxMCE how you want to respond to a fire, security breach, etc. You can see that when there is a security breach you want to sound a siren, turn on all the lights, sprinklers and TV's and play a menacing audio file. On the Wizard/Security/ Cellphone Notifications page you indicate how you want LinuxMCE to notify you of any security problems and who should be notified that sensor is tripped and the sensor is "Armed".
LinuxMCE can also be put in "Monitor Mode", aka Baby Sitter mode. This is really a special, hidden mode that has nothing to do with the 6 security modes. You can turn monitor mode on whether the house is armed, disarmed, entertaining, etc. "Monitor Mode" means that every time a sensor with monitor mode checked is tripped you will be notified on your mobile phone with a picture--whether or not it sounds an alarm. A common use of monitor mode is when you leave the children at home with a baby sitter. The fact that the house is in "Monitor Mode" is not indicated on the Orbiters anywhere. It is like a 'hidden' mode--the baby sitter will only see that the alarm system is disarmed, or armed at home, or whatever security mode you have chosen and will not know that the house is being monitored. The security system will still react like normal. Monitor Mode is just an additional layer. You can check off monitor mode, for example, for the primary door sensors. Then, even if those sensors are not armed and do not sound the alarm, you will still be shown a picture on your mobile phone whenever the sensor is tripped so you can be sure there are no unauthorized visitors. Just check "Monitor Mode" for every sensor you want to monitored when you leave the house in this mode.