Pattern
The phone is part of the device
Architectures where a smartphone or wearable is a component of the medical device, not a companion screen. It removes hardware and adds obligations, and the trade is only worth making with both sides written down.
Two architectures that look alike
Claim: observation
In the first, the phone is an accessory: it displays and syncs, and the medical function lives entirely in the dedicated hardware. In the second, the phone is part of the device: its sensors, compute, or radio are inside the measurement or the safety path.
The second removes a screen, a battery, a radio, and a housing from the bill of materials. It also brings an uncontrolled platform inside the device boundary: an operating system that updates without asking, hardware that varies by model, a battery the user manages, and permissions the user can revoke.
What the trade actually costs
Claim: hypothesis
A supported-handset list, and the testing that keeps it honest. A response to platform updates that behaves like change control rather than a support ticket. Degradation behavior when a permission is withdrawn or a sensor is unavailable. Cybersecurity assumptions that hold on a device the manufacturer does not control. Human factors testing on the phone the patient actually owns.
Our current reading, and it is a hypothesis rather than a conclusion: the phone-as-component architecture is worth it when the phone contributes a capability that would otherwise be expensive to reproduce, and not worth it when it only saves a display.