Burgar Alarm -evaluation zone (Loop)?

Do you know how professional alarm system, perhaps by DSC, evaluate the state of the loop?
I'm thinking about their own alarm with ARM MCU and I would had learned by professionals.
According to the manual loop can have the following states:
0Ω (shorted wire, loop shorted) Status Fault
5600Ω (contact closed) Status Secure
Infinite (broken wire, loop open) Status Tamper
11200Ω (contact open) Status Violated
loop probably looks something like this,
the question is how to evaluate the condition of

the question is how to evaluate the condition of

Click to expand...

How about a voltage measurement?

Redraw your circuit so it makes sense. A Vsupply, feeding a Rsupply, this feeds the alarm circuit and is connected to the centre of a one pole four way switch. Between each pole and the common, you have a different resistor. A short circuit (bad), a 5600 ohms (good), a 11200 (bad), open circuit (bad).
The alarm circuit should have a decoupling capacitor and a catching diode. As FvM said, if you measure the voltage you can find out the alarm state. So if you have a micro with Polling analogue inputs you have cracked it. Or make sure the voltage outputs are with the range of your ADC, and use analogue transmission gates to poll the inputs. Or if no micro (hard wired logic) you will need some at least 3 voltage detectors per input.
Frank

Thank you for the response. Measure the voltage of course occurred to me as well.

Classical hardwired alarm systems used to have comparators for loop status evaluation. But they are obsoleted by microcontrollers with ADC function.