Many people simply use a z-wave Magnetic Contact Sensor with external contacts. You simply need to close/open those contacts electrically (e.g. via dry contact relay) to change the state from Open to Closed. (i.e. don’t use the magnetic switch portion of the sensor, just the external contacts.)
No need to “monitor current flow” as that is much more complicated that simply opening or closing a set of contacts.
Here is an example where someone used one of these sensors to create a water leak sensor, as an example of what is possible.