There are some systems that are non-electrical and I can not tell you about those, but on the ones with a break away SWITCH (Electrical) it is a SPST normally closed clothspin type switch with something between the "Jaws" to prevent it from closing,,, (the plastic plug).
you pull the plug the jaws snap closed and the circuit is complete.
Near as I can tell they all work that way.
HOWEVER: sticking with OEM means that if the system fails, they can not stand there as 3 technicians did one day in my office and say "It is HIS FAULT" it does not work (each pointing to someone else).
The next day (One of them proved who's fault it was) it worked.
Home is where I park it!