What's the point of more than two gateway security systems?

In Uplink, the later gateways have space for 3-4 security systems, but there's only two security systems available (motion sensor and self destruct). Having both security systems is useful so you can detect activity and nuke your gateway, but is there any advantage to having more than one of each type?

Solution 1:

There is no point in having more than 1 motion sensor and 1 self-destruct device. In fact, you can remove the need for a self-destruct device in your later computers by using the Revelation virus to destroy it rather than a bomb (version 1 does not spread and so is functionally equivalent to a self-destruct device).