It might be best to bring this to the doctor’s attention and have him/her address it. Or even having your doctor do a “review session” with both of you and then having him/her watch each of you practice on each other, with the doctor pointing out that the power needs to be on, might be best. I say this because some people don’t take constructive criticism well and it it could cause problems between you two. Now if your doctor isn’t worried about it and doesn’t want to do something, I would remind the doctor that if the unit isn’t on and the patient is being billed for the service, it could be seen as fraud.