Yes it should be prescribed (logged), or else how do you know how they are getting better or worse if SATS, ECG, BP or whatever else you are monitoring etc drop or increase.
Community based patients (and or their carers)should be given documented training on what to do, who to contact if there is a problem etc.
As far as private goes, there are thousands out there on variuos devices and suppliments that havent been prescribed by a healthcare professional you cant be responsible for these candidates if they decide to do what they want in confinement.
Other than legislating to stop the purchase.