Lessons Building WearOS Apps

Developing applications for smartwatches presents unique challenges compared to mobile phones. The foremost constraints are battery cell capacity and screen boundaries.

The 15% Battery Saver Rule

Smartwatch battery capacities are typically under 450mAh. A poorly optimized background service drawing only 10mA extra current can drain the device in hours. We formulated constraints to restrict active CPU usage to transient intervals (under 5 seconds) during alerts.

Continuous polling of accelerometer or PPG (heart rate) sensor values keeps the application processor awake. Instead, use the Android sensor batch API to allow hardware sensor hubs to collect readings in hardware FIFOs and flush them to the app in batches every 10–20 minutes.