This code system http://hl7.org/fhir/operational-status defines the following codes:

CodeDisplayDefinition
offOffThe device is off.
onOnThe device is fully operational.
not-readyNot ReadyThe device is not ready.
standbyStandbyThe device is ready but not actively operating.
transduc-disconTransducer DiconnectedThe device transducer is diconnected.
hw-disconHardware DisconnectdThe device hardware is disconnected.
entered-in-errorEntered In ErrorThe device was entered in error.