You can setup SHM security with just one dummy sensor which will make the arm / disarm buttons appear again without the alarm actually being functional (just an empty shell to give you an easy way of changing alarm mode)
Then use the CoRE Smart App to respond to events instead.
SHM is armed
(Any of XYZ Contact changes to open OR Any of XYZ Motion changes to active)
Shoot intruder with nail gun
CoRE install guide and link to the CoRE wiki in post one of the following thread: