Broadcasting

Turn the device itself into a beacon.

services.AddBeaconBroadcasting();

var access = await broadcaster.RequestAccess();
if (access != AccessState.Available)
    return;

await broadcaster.StartIBeacon(uuid, major: 1, minor: 2);

// or Eddystone
await broadcaster.StartEddystoneUid(EddystoneUid.Parse("0102030405060708090A", "0B0C0D0E0F10"));
await broadcaster.StartEddystoneUrl("https://shinylib.net/");

broadcaster.Stop();

Only one advertisement runs at a time — starting a second replaces the first.

Transmit power

The optional txPower argument is the value a receiver calibrates against: “this is how strong I measure at the reference distance”. It does not change the radio’s actual output power, which no platform exposes. Getting it wrong skews every receiver’s distance estimate.

Defaults are -59 dBm for iBeacon (measured at 1 metre) and -18 dBm for Eddystone (measured at 0 metres). If you are broadcasting for real use rather than testing, measure it.

Platform support

Platform	iBeacon	Eddystone
iOS / Mac Catalyst	Yes	No
macOS	Yes	No
Android	Yes	Yes
Windows	Yes	Yes
Linux	Yes	Yes
Blazor WASM	No	No

Apple cannot broadcast Eddystone

CoreBluetooth’s startAdvertising reads exactly two keys — a local name and a list of service UUIDs — and silently discards everything else in the dictionary. There is no way to put service data on the air, and Eddystone is service data. StartEddystoneUid and StartEddystoneUrl throw PlatformNotSupportedException there rather than appearing to succeed.

iBeacon works because Apple exposes a dedicated advertisement key for exactly that purpose.

Apple stops broadcasting a usable beacon in the background

When the app is backgrounded, iOS moves the advertisement into an “overflow” area that only another iOS device explicitly scanning for the same service UUID can see. It is no longer a beacon any other device can decode. Plan for foreground-only broadcasting on Apple platforms.

Linux

BlueZ inverts the model every other platform uses. Rather than handing a payload to an API, the application exports a D-Bus object describing the advertisement and registers its path with org.bluez.LEAdvertisingManager1; BlueZ then calls back into your process to read the properties, and calls Release() on that object when it drops the advertisement. Shiny does all of that for you, but two consequences leak through and are worth planning for:

• The process has to stay alive and connected to the system bus for the advertisement to keep running. There is no fire-and-forget: if your app exits, BlueZ has nothing left to read from.
• BlueZ can stop the advertisement on its own — the adapter powering down, bluetoothd restarting, or another client taking the last advertising slot. Shiny honours the resulting Release(), so IsAdvertising goes false rather than getting stuck on, and you can start again.

The adapter caps how many advertising instances run at once (LEAdvertisingManager1.SupportedInstances). When it is full, RegisterAdvertisement fails and the exception carries BlueZ’s own reason.

Building the payload yourself

If you are advertising through IBleHostingManager directly rather than through IBeaconBroadcaster, use IBeaconPacket (in Shiny.BluetoothLE) or EddystoneBuilder to build the bytes:

var payload = IBeaconPacket.Build(uuid, major, minor, txPower: -59);

await hosting.StartAdvertising(new AdvertisementOptions
{
    ManufacturerData = new ManufacturerData(IBeaconPacket.AppleCompanyId, payload),
    IsConnectable = false
});

Never hand-roll an iBeacon payload

Every multi-byte field in an iBeacon advertisement is big-endian. Guid.ToByteArray() and BitConverter.GetBytes() are both little-endian on every platform Shiny targets, so building the packet with them ships a byte-swapped UUID, major and minor that no receiver can match. This is not hypothetical — it is the bug AdvertiseBeacon shipped with before 5.6.0.

Permissions

• iOS / Mac Catalyst / macOS — NSBluetoothAlwaysUsageDescription in Info.plist
• Android — android.permission.BLUETOOTH_ADVERTISE
• Windows — the bluetooth capability for a packaged app, and an adapter that supports the peripheral role (BluetoothAdapter.IsPeripheralRoleSupported)