Devices that are not shared, which can be connected only to host or guest but not to both at the same time, are normally always released, disconnected from guest and reconnected to host when vm is closed.
If you close a vm with some of these devices still connected, next time you start the vm they are again automatically disconnected from the host and reconnected to guest. In this case you get a warning:
If you do not let vm to reconnect the device (click Cancel), you must manually reconnect it when needed:
To monitor your device status, you use the statusbar icons as these images show: