Hot-Cold Finder
Proximity, Feedback, and Real-Time Sessions in iOS 26
Most apps begin with intent. A user taps a button, selects an item, or navigates to a screen, and the system responds. Hot-Cold Finder begins somewhere else entirely. It reacts to movement, distance, and physical space, and it does so continuously rather than in discrete steps. That difference changes how the app is structured, how the UI behaves, and how the system is allowed to participate.
Hot-Cold Finder exists to explore what happens when an app stops waiting for input and instead listens to a signal. In iOS 26, that signal can be proximity itself. Nearby Interaction makes distance measurable, but more importantly, it makes it actionable. This app is not about precise measurements or novelty hardware. It is about understanding how iOS supports experiences that operate in real time, across devices, and under constantly changing conditions.
Why Proximity Is a Different Kind of Problem
Proximity-based interactions don’t fit neatly into the patterns most apps rely on. There is no form to submit, no list to update, and no stable state to persist. Instead, there is a stream of information that changes as the user moves. The app must respond immediately, smoothly, and predictably, even though the underlying signal is noisy and transient.
That makes proximity an ideal problem space for studying iOS 26 beyond traditional app flows. Distance updates arrive continuously. Sessions can drop without warning. The system enforces constraints that the app cannot override. Building something useful in that environment requires restraint, clear responsibility boundaries, and a willingness to treat feedback as more important than precision.
The Problem Space: Finding Without Seeing
Hot-Cold Finder is intentionally simple. One device acts as a target. Another device moves through space. Feedback tells the user whether they are getting closer or farther away. There is no map, no coordinates, and no numeric distance displayed by default.
That abstraction is deliberate. Raw distance values are technically interesting, but they are not always helpful. A “hotter or colder” signal reduces cognitive load and allows the user to focus on movement rather than interpretation. It also creates room for different kinds of feedback, whether visual, haptic, or auditory, without tying the experience to a specific measurement unit.
By keeping the task human and intuitive, the app surfaces the real challenges of proximity-based design without hiding them behind UI complexity.
Architecture Under Real-Time Pressure
Hot-Cold Finder uses the same Model–View (MV) architectural posture as the other apps in this series, but it applies it under very different conditions. In this context, MV means that models represent session state, views render feedback, and services manage the lifecycle and behavior of the interaction itself.
There is no persistence layer driving this app. State is session-bound and ephemeral. When the session ends, the state disappears with it. Services own the Nearby Interaction session and the MultipeerConnectivity coordination, while views respond to changes in signal strength rather than explicit state transitions.
This structure keeps the app responsive without becoming brittle. Views do not attempt to manage timing or distance calculations. Services do not concern themselves with presentation. Each layer does one job, even while updates arrive continuously.
Architecture here is again treated as an optimization problem, not a stylistic preference.
Nearby Interaction as a Session, Not a Feature
Nearby Interaction is often described as a feature, but treating it that way undersells what it actually is. At its core, it is a session-based capability that requires negotiation, trust, and coordination between devices. Tokens must be exchanged. Sessions must be established and monitored. Failures must be expected.
In Hot-Cold Finder, MultipeerConnectivity handles peer discovery and token exchange. Nearby Interaction then takes over to provide distance updates once the session is established. This separation of concerns keeps each system doing what it does best. MultipeerConnectivity handles discovery and communication. Nearby Interaction handles spatial awareness.
The important takeaway is that proximity is not something you turn on and forget. It is something you manage carefully for as long as the session exists, and then release cleanly when it ends.
Feedback Loops Over Screens
Once distance data starts flowing, the design question shifts quickly from accuracy to usefulness. A constantly updating numeric value is rarely what the user needs. What they need is directional feedback that responds immediately to movement.
Hot-Cold Finder treats UI as a feedback surface rather than a destination. Visual cues change as proximity changes. The UI remains minimal so the signal stays clear. The app does not ask the user to interpret numbers while moving. It reacts with them instead.
This approach also leaves room for future extensions. Haptics, sound, or other modalities could be layered on without changing the underlying architecture. The core idea remains the same, feedback should guide motion, not demand attention.
What Hot-Cold Finder Teaches About iOS 26
Building Hot-Cold Finder reinforces several realities about modern iOS development. Not every app benefits from persistence. Not every experience revolves around navigation or screens. Some of the most interesting system capabilities operate continuously and invisibly, responding to the physical world rather than explicit user intent.
iOS 26 supports these kinds of experiences, but it also demands discipline. Sessions must be managed. Signals must be interpreted thoughtfully. UI must stay out of the way. When those constraints are respected, the platform enables interactions that feel immediate and natural rather than fragile or forced.
Real-time systems reward clarity and restraint more than cleverness.
Closing Thoughts
Hot-Cold Finder occupies a very different space than the previous apps in this series, but it follows the same principles. It isolates a specific capability, explores it under real constraints, and avoids unnecessary abstraction. The result is not a polished product, but a clear understanding of how proximity-driven experiences behave on modern Apple platforms.
The next article shifts again, this time toward background execution and system trust with Daily Quote Fetcher. The surface changes, but the discipline remains the same.
If you want to explore the full implementation details, including session management, peer discovery, and proximity handling, you can find the complete code here:
GitHub: https://github.com/initMoin/portfolio/tree/main/HotColdFinder