BBB Business Review

Sensor Activity Monitoring interactive accounts are capable of monitoring the activity on up to 50 sensors by default. This feature is not related to the systems ability to operate sensors, but rather's ability to notify you about specific sensors. This means you can set up notifications to alert you when any of those 50 sensor are opened. Generally this is used for door and window sensors when placed on high priority points of entry or egress. 

If you do have a very large system you can increase the number of sensors that you are able to monitor the activity of. There is no limit to the maximum number of sensors your are able to have activity monitoring on.