Door Strike relays from separate controllers can be used to control a single door. This is not recommended but in some rare cases it makes sense e.g. using a V2000 two door HID VertX controller to control a single door with and IN and OUT reader for time and attendance. The following diagram is self explanatory…
![](https://www.middleware-associates.com/wp-content/uploads/2018/09/ds_parallel_relay-293x300.png)