Good.
While serialized parts allows a record of the repairs and replacement parts on a device, which is especially nice when buying used and refurbished, the hijacking of functionality is the real crime. Screen replacements, for example, on the iPhone 14 series, even when using genuine Apple parts and without "re-pairing" by a certified technician or through SSR, results in the loss of True Tone, auto-brightness, and other critical functionality.
Here's an (incomplete) list of some of the functionality lost when doing a replacement of said part, even when parts are genuine, off of the top of my head:
1. Battery -> loss of battery health metrics
2. Display -> loss of auto-brightness, True Tone, and Face ID
3. Camera -> loss of portrait mode, buggy Camera app functionality, and loss of optical zoom
There is no technical reason why this should be the case - based on teardowns and hardware analysis even -
other than to make non-genuine parts so crippled to discourage self repair, third party repair or to encourage a device upgrade.
EDIT: Some posts below mention the "theft deterrence" argument, where serialized parts may discourage iPhone thefts by making their parts less valuable by inhibiting functionality. There is no evidence to suggest that this is an effective theft "deterrent". In fact, iPhone thefts are up and parts are still being sent to China in record numbers, even with these "deterrents".
I won’t address your mentions above on Face ID in #2 and the camera in #3 as I don’t have technical experience in those areas.
I will address the
battery and loss of health metrics. The discharge curve of lithium batteries makes estimating remaining life and health very difficult. Such batteries retain their voltage rather steadily until they are nearly exhausted and their voltage drops off very severely. Traditionally, voltage is used to estimate remaining capacity, which make that estimate very difficult when you know the manufactured capacity, estimated impurities, etc… For most of the discharge, it appears the battery is near 100% until it nears the end of its capacity and it very quickly drops to 0%. When someone places a battery into the system that may or may not be new and may not meet the OEM tolerances, it becomes impossible to estimate. I do think Apple uses a more complex method to estimate remaining capacity. I don’t have access to their software, but what I’ve observed indicates they’re using number of cycles the battery has experienced, estimated consumption from charged, estimated completion of last charge, and some feedback for the case the battery dies before they estimated it would. A wise (or even mildly wise) engineer would use OEM tolerances and design information to calculate battery life and health. A random battery placed in the system could be noticeably different. If Apple used their calculations for OEM batteries on other batteries, systems would start experiencing unexpected and uncontrolled shut-downs as well as shutdown before they noted to the user shutdown was imminent.
The battery challenge is greatly exacerbated in today’s mobile products because instantaneous power draw can vary incredibly. The processors have very complex and extensive power-saving modes and a number of peripherals that can be shutdown. For Apple’s processors, we don’t have the details; however, I suspect they are at least as complex as TI’s OMAP processors with which I have worked. If the battery is near the end of its capacity, a power spike can easily cause the product to shut down unexpectedly as the system draws more power than the battery can reliably support, the voltage on the battery drops below the allowed (safe) threshold, and the system shuts down with no chance to save unsaved work, close files, close connections, etc… Preventing this on an unknown battery is impossible.
Regarding autobrightness and truetone on the
display, displays from different manufacturers and even from a given manufacturer can vary significantly in brightness and color. If Apple used parameters for their OEM display on a random display, it could easily be a poor user experience as the random display would likely not have the same characteristics.
Your comments suggest that Apple is using commodity (widely available parts). Apple is known for working very closely with their suppliers to create a very specific user experience. For the significant parts (outside of popcorn parts/basic resistors, capacitors, etc…) they use custom parts. This doesn’t allow a person to grab a part off the shelf and expect the same user-experience or functionality with the software — even when the part works electrically in the system.
Edit: I meant to add note of your comment of use of genuine parts… First, Apple has to have a way of identifying “genuine”; making sure the part has the “code” or serial number when installed no a given device is one way of doing that. Further, there has been suspicion published on MacRumors before that Apple calibrates some displays to a device to provide some of the capabilities they offer. This could be particularly likely for Reference Mode, which you don’t mention. It could be true of Truetone.
Finally, I do agree with those that note theft deterrence as a further reason Apple does this. You are right that incidents of chopping phones for parts have been going up. That doesn’t necessarily mean Apple’s approach in this space doesn’t hold back this increase. At the insistence of the NYPD and other law enforcement agencies, Apple developed the Find My lock, which reduced the number of stolen phones dramatically. Some time ago, they started seeing a rise of parts being sold from phones that were locked. Requiring serial number matches will decrease the attractiveness of parts that don’t match making those who buy stolen parts (intentionally or unintentionally) less satisfied (as you note your dissatisfaction with Apple’s disabling of some functions for mismatched parts above). Apple’s relatively high repair prices are probably (and the discovery by some that they can take parts out of stolen phones and sell them) the reason the number of stolen devices has risen again.