It's an entire system option Mac: AOA DIsagree is part of the AOA Indication package. Non fliers with spec lists have a long history of boosting their careers with such savings.
Danny and I got together when I was being shouted down that, in the normal world, the B757 had its batteries linked via a relays and cable for total generator loss. 90% plus US forum called Avsig doing the shouting. I supplied a US big three airline senior maintenance man in SFO with the exact drawings from the official Boeing maintenance manual plus the registrations of three US registered aircraft inherited from a failed lease to Australia which had the connected batteries. Two relays, one cable but everything else needed was already fitted on the production line.
In the mid nineties it was still career building to strike even dual position light bulbs off the options list from Boeing. I'm sure you've met these people in medicine.