JP,
You're good at trolling.
Where do you get vandalism?
Removing a detector (or disconnecting the tandem wire) from the loop simulates a failure of the unit.
In your specific install and example, I can remove every detector on the loop except for the one you installed your "supervision" relay at and whichever one is connected to the panel, simulating a failure of connected devices.... and using your installation methodology and practices, the connected system does not know there is any issue with the loop. Same with the opposite side of the relay coil, there is no supervision possible to detect a failure besides performing routine testing, but that will not address if there were a transient that welded the contacts after the last test performed, there is no way for the system to detect and supervise for that failure mode....this is why the relays and connections to FACP's for primary notification are commonly frowned upon and almost every one of the relays are not listed for the purpose and the majority of the detectors also state to NOT connect them to any system with a control panel.
I agree 100% with Gizzmo...and hope you have a very lenient insurer.