Device discovery

The SDK finds, permissions, and tracks the USB reader so your app doesn’t touch UsbManager directly. This is handled by ReaderManager, returned from sdk.startReaderDiscovery().

The flow-driven model

ReaderManager exposes three flows you collect from your UI:

readers: StateFlow<List<ReaderInfo>> — currently connected and permissioned readers. Emits on attach, detach, and permission changes.
permissionGranted: StateFlow<Boolean> — true once a supported reader has USB permission.
readerErrors: SharedFlow<SladeIDError> — discovery/permission failures (vendor init CaptureError, permission-denial AuthError).

[!NOTE] A reader that is simply not plugged in is not an error — it never appears on readerErrors. That lets you show an accurate “no reader connected” message instead of guessing from an empty readers list.

Lifecycle

On startReaderDiscovery() the manager:

Registers a single broadcast receiver for USB permission, attach, and detach events.
Fast-paths any already-permitted supported device (fixes the “unplug/replug or restart” case).
Requests permission for the rest.
On any grant/attach/detach, re-probes every supported vendor by construction and republishes readers.

Only one reader is expected at a time (USB bus power), so a full re-probe per event is cheap.

Permissions

USB permission is a system dialog. Two paths grant it:

Manifest device_filter — when the reader is attached, Android shows the permission dialog and routes the attach intent to your activity. This is the standard grant for SecuGen and BioMini. Re-requesting those in code breaks their vendor-SDK listing, so the SDK deliberately doesn’t.
manager.requestPermissions() — a one-shot, user-driven request for every attached supported reader that lacks permission (covers EADAK / Aratek, and SecuGen/BioMini for hosts that don’t wire a device_filter). Call it when your activity receives a USB attach intent or from a “connect” button. Already-permitted devices are skipped, so it never re-prompts.

Reader auto-detect on customized Android builds

Some manufacturer-customized Android builds deliver USB_DEVICE_ATTACHED only to a manifest-registered <receiver>, not a runtime one. If auto-detect works on stock Android but not on a particular device, register a manifest <receiver> for the USB attach action and route it to a discovery refresh (requestPermissions() + refreshDevices()).

Supported vendors

ReaderManager probes SecuGen, Suprema BioMini, and EADAK / Aratek TrustFinger by default, each behind the common FingerprintReader abstraction. Vendor IDs and models are in the device support matrix.