Eddystone

Eddystone is Google’s open beacon format. Unlike iBeacon it travels as service data under UUID 0xFEAA, which every platform hands to the app untouched — CoreBluetooth included. That makes it the one beacon format that behaves identically everywhere.

services.AddEddystoneScanning();

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

var sub = scanner.WhenFrameReceived().Subscribe(frame =>
{
    switch (frame)
    {
        case EddystoneUidFrame uid:
            Console.WriteLine($"{uid.Uid.Namespace}/{uid.Uid.Instance} at {uid.Distance:N1}m");
            break;

        case EddystoneUrlFrame url:
            Console.WriteLine(url.Url);
            break;

        case EddystoneTlmFrame { IsEncrypted: false } tlm:
            Console.WriteLine($"{tlm.BatteryVolts}V {tlm.TemperatureCelsius}°C, up {tlm.Uptime}");
            break;

        case EddystoneEidFrame eid:
            Console.WriteLine($"EID {eid.EphemeralIdHex}");
            break;
    }
});

The scan is filtered to 0xFEAA, which is also what lets it keep delivering results when an iOS app is backgrounded — CoreBluetooth delivers nothing in the background from an unfiltered scan.

Frame types

UID — identity

A 10-byte namespace naming the deployment and a 6-byte instance naming the individual beacon within it.

var uid = EddystoneUid.Parse("0102030405060708090A", "0B0C0D0E0F10");

// EddystoneUid is a value type - compare it directly
if (frame.Uid == uid) { }

Namespace is 20 hex characters, Instance is 12.

URL — a compressed web address

Eddystone squeezes a URL into 17 bytes by substituting one byte for the scheme and another for any of thirteen common top-level-domain endings. Shiny decodes it for you; EddystoneUrlFrame.Url is the expanded form.

EddystoneUrlCodec is public if you need the compression directly — Encode(url) throws with a clear message when a URL will not fit, rather than silently truncating.

TLM — telemetry about the beacon itself

case EddystoneTlmFrame tlm when !tlm.IsEncrypted:
    // BatteryVolts is null on a mains-powered beacon, not 0
    // TemperatureCelsius is null when no sensor is fitted, not 128
    Console.WriteLine($"{tlm.BatteryVolts:N3} V");
    Console.WriteLine($"{tlm.TemperatureCelsius:N1} °C");
    Console.WriteLine($"{tlm.AdvertisementCount:N0} advertisements since power-on");
    Console.WriteLine($"up for {tlm.Uptime}");
    break;

The spec reserves 0 millivolts for “mains powered” and 0x8000 for “no temperature sensor”. Shiny surfaces both as null rather than as a flat battery and a 128°C beacon.

Encrypted TLM (version 0x01) is handed back intact in EncryptedPayload for a caller that holds the beacon’s identity key.

EID — a rotating identifier

EddystoneEidFrame.EphemeralId is the raw 8 bytes, with EphemeralIdHex for convenience. Resolving one back to a registered beacon needs the deployment’s identity key and the Curve25519 / AES-EAX derivation from the Eddystone-EID specification, which Shiny does not implement.

Correlating frames from one beacon

A beacon interleaves frame types — you will see a UID frame, then a TLM frame, then a UID frame again. The only thing tying them together is the transmitting peripheral:

var byBeacon = new Dictionary<string, BeaconHealth>();

scanner.WhenFrameReceived().Subscribe(frame =>
{
    var health = byBeacon.GetOrAdd(frame.PeripheralId);

    if (frame is EddystoneUidFrame uid)
        health.Uid = uid.Uid;

    if (frame is EddystoneTlmFrame tlm)
        health.BatteryVolts = tlm.BatteryVolts;
});

Transmit power and distance

Eddystone calibrates at 0 metres, iBeacon at 1 metre

The two formats use different reference distances — a 41 dBm difference. Shiny accounts for it when estimating distance, so an Eddystone TxPower and an iBeacon TxPower are not comparable numbers. Do not “fix” one by matching it to the other.

Everything on the Distance & Accuracy page applies to Eddystone too, including the RSSI filtering — and unlike iBeacon on Apple platforms, it applies on every platform, because Eddystone always comes through the BLE scan rather than CoreLocation.

Permissions

Eddystone is a plain BLE scan on every platform:

• iOS / Mac Catalyst / macOS — NSBluetoothAlwaysUsageDescription in Info.plist
• Android — BLUETOOTH_SCAN with usesPermissionFlags="neverForLocation"
• Windows — the bluetooth capability for a packaged app