Chronos is a smart disc intended to be attached to the back of any analog watch. With a dedicated app on a smartphone, it can be used to control music, get reminders, count steps and calories burned, control the phone’s camera shutter and more.


Business type

Internet of Things, Wearables


  • Digital Strategy
  • UI/UX Design
  • Android Development
  • Front & Back-end Web Development

Product description

Chronos is a 3mm thick disc that mounts on the back of almost any watch. A user connects it with their smartphone via Bluetooth and then can use it to track steps, get notifications, silence calls, tap it to find the phone and more.


  • The Android app was first expected to be a clone of the iOS app. But it needed to be additionally adjusted to the platform’s guidelines and users’ habits.
  • The Chronos app was required to work with firmware that was not fine-tuned and finalized at that moment.
  • The app sports smart gestures and notifications. To make them possible, the app needs to keep a stable, long-term connection with the Chronos disk. BLE APIs, battery consumption and connectivity management restrictions made its implementation a tough task.
  • The app includes a customizable notifications manager. It lets users create unique sets of notification patterns for their instance of the app.


  • The app establishes long-term connection between the smartphone and the disc. We implemented it on the Android SDK level. Such approach is more flexible than a default system-level connection.
  • The app must regularly show notifications to keep the connection established. We used notifications as one more way of UI input to communicate with the user about the most urgent events.
  • Android OS doesn’t provide enough system permissions for third-party apps. We were able to overcome these challenges while keeping the UX smooth and positive.
  • A custom app notification parsing mechanism keeps the highest level of privacy. Even the app itself doesn’t know what text the notifications will show next. Users can also set the vibration type and color of the notifications to customize them even more.
  • Following current healthy lifestyle trends, Chronos also supports Google Fitness. It allows sharing data with other fitness apps.
  • Our developers gained deeper expertise with Android BLE APIs, known for many pitfalls.
  • We improved Nordic DFU mechanisms to make the device firmware update process even smoother.
  • Modern programming is reactive. We utilized best ReactiveX approaches and used RxJava2 to let parts of the app communicate with each other in the most effective way.
  • We translated the Design Team requirements into smooth and sound custom views. That allowed us to provide users with the highest-level user experience they love.

Tools used

Java, Android SDK, RxJava 2 for reactive communications, Dagger 2 as a dependency injection framework, Fabric Crashlytics as a crash analytics to keep the high level of quality even after release.

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