Background mode
A declared, tightly limited reason the OS lets an app keep doing a specific job after it leaves the screen.
See it
What it is
A background mode is a declared reason the operating system recognizes for letting an app do limited work after it leaves the screen. Audio playback, active navigation, Bluetooth communication, and scheduled refresh are different modes with different rules. The audio mode is why Spotify keeps playing with the screen off, and the location mode is why Google Maps keeps calling turns from a pocket. Declaring one opens a narrow lane; it does not turn a phone app into an always-running server.
Reach for the mode that matches a feature users can see and understand. On iOS, Xcode writes selected capabilities into UIBackgroundModes and specialized APIs do the work. On Android, long visible work commonly uses a foreground service with a declared service type and an ongoing notification, while deferrable jobs belong in WorkManager.
Gotcha: declaring extra modes does not buy extra runtime. The OS can suspend or kill the process, stores review whether the declaration matches the feature, and misuse drains batteries. Persist progress, handle interruption, and remove a mode when the feature that justified it is removed.
Ask AI for it
Implement the smallest background capability this feature needs. On iOS, add only the matching UIBackgroundModes value and use BGTaskScheduler for deferrable refresh. On Android, use WorkManager for deferrable work; if continuous user-visible work is truly required, create a foreground service with the exact android:foregroundServiceType and an ongoing notification. Persist a checkpoint before suspension, resume idempotently after process recreation, stop every task and service when its user-visible job ends, and document which screen or setting proves the declared mode is used. Do not add audio, location, Bluetooth, or VoIP modes unless this feature actively performs that job.