diff --git a/lib/src/oura.dart b/lib/src/oura.dart
index 0b7a7a8..249dd14 100644
--- a/lib/src/oura.dart
+++ b/lib/src/oura.dart
@@ -99,6 +99,10 @@ const int kOuraEvtTemp = 0x46;
 /// A single skin-temperature reading.
 const int kOuraEvtTempPeriod = 0x69;
 
+/// The RTC beacon, a wall-clock anchor the ring emits on its own. See
+/// [decodeRtcBeacon].
+const int kOuraEvtRtcBeacon = 0x85;
+
 /// Firmware diagnostics. Subtype-multiplexed; see [decodeDebugData].
 const int kOuraEvtDebugData = 0x61;
 
@@ -127,6 +131,21 @@ int? decodeTimeSync(OuraEvent e) {
   return (v >= 1700000000 && v <= 4100000000) ? v : null;
 }
 
+/// Unix seconds from an `rtc_beacon` (`0x85`) body, or null when [e] is not
+/// one or the value is not a date.
+///
+/// Layout: `u32` LE Unix seconds at offset 0, then reserved bytes and a `u16`
+/// at offset 8 whose meaning is unknown. Bodies under 10 bytes are refused.
+/// Same date window as [decodeTimeSync], so an unset RTC never becomes an
+/// anchor.
+int? decodeRtcBeacon(OuraEvent e) {
+  if (e.tag != kOuraEvtRtcBeacon || e.body.length < 10) return null;
+  final v = e.body.buffer
+      .asByteData(e.body.offsetInBytes)
+      .getUint32(0, Endian.little);
+  return (v >= 1700000000 && v <= 4100000000) ? v : null;
+}
+
 /// Skin temperature in degrees Celsius, one entry per probe.
 ///
 /// The wire carries signed 16-bit little-endian CENTI-degrees. Anything outside
diff --git a/test/oura_test.dart b/test/oura_test.dart
index 010b6cb..aee42b0 100644
--- a/test/oura_test.dart
+++ b/test/oura_test.dart
@@ -243,6 +243,23 @@ void main() {
           parseOuraFrame(_hex('4208') + _hex('01000000') + _hex('00000000'))!)!;
       expect(decodeTimeSync(unset), isNull);
     });
+    test('an rtc beacon is a little-endian unix second', () {
+      final ok = parseOuraEvent(parseOuraFrame(
+              _hex('850e') + _hex('01000000') + _hex('4fd2376a00000000e803'))!)!;
+      expect(decodeRtcBeacon(ok), 1782043215);
+      // A body too short for the full layout is not a beacon.
+      final short = parseOuraEvent(parseOuraFrame(
+              _hex('8509') + _hex('01000000') + _hex('4fd2376a00000000'))!)!;
+      expect(decodeRtcBeacon(short), isNull);
+      // A different tag is not a beacon either.
+      final other = parseOuraEvent(parseOuraFrame(
+              _hex('420e') + _hex('01000000') + _hex('4fd2376a00000000e803'))!)!;
+      expect(decodeRtcBeacon(other), isNull);
+      // An unset RTC is not an anchor.
+      final unset = parseOuraEvent(parseOuraFrame(
+              _hex('850e') + _hex('01000000') + _hex('0100000000000000e803'))!)!;
+      expect(decodeRtcBeacon(unset), isNull);
+    });
   });
 
   group('outbound frames', () {