Is it possible to connect my securitySensor up in series, if I wanted to monitor a number of doors in the same building for example? If so, how do I do that?

Yes, the securitySensor can actually be wired in sequence. You can take the contact from one security sensor and wire it to the next. The only limit to the number of sensors you can have in series is the maximum run length of the Security Sensor, which is 300 meters, or about 1,000 feet. You have a couple options. You can connect the security sensor, from each door to each extra dry contact input (X20). The advantage of this solution is that if you have 20 doors you can label each one individually and see which one has triggered. With them wired in sequence you will know a door has opened but not which door.