diff --git a/lib/src/onehz/human/event_detection.dart b/lib/src/onehz/human/event_detection.dart
index 32bac50..abf5164 100644
--- a/lib/src/onehz/human/event_detection.dart
+++ b/lib/src/onehz/human/event_detection.dart
@@ -44,6 +44,12 @@ import '../types.dart';
 import '../util.dart';
 import '../foundations/baseline.dart';
 
+/// Nightly RHR is read in whole bpm; a baseline whose SD sits below this
+/// quantum has no dispersion the instrument can actually resolve — see
+/// [dispersionBelowQuantum]. Same convention as illness_cusum.dart and
+/// readiness_composite.dart's `rhrInput` (quantum: 1).
+const double _rhrQuantum = 1.0;
+
 /// One night's nocturnal summary vs the personal baseline window.
 class NightSignature {
   final double rhr; // nocturnal RHR tonight (bpm)
@@ -135,12 +141,21 @@ Metric<EventState> alcoholNightFlag(
   final rmsBase = robustBaseline(rmssdHistory, minValid: minNights);
   final rhrDelta = tonight.rhr - (rhrBase.center ?? tonight.rhr);
   final rmssdDelta = tonight.rmssd - (rmsBase.center ?? tonight.rmssd);
-  final rhrZ = rhrBase.modZ(tonight.rhr);
+
+  // Nightly RHR is read in whole bpm; a baseline whose SD sits below this
+  // quantum (quantized-but-nonzero, e.g. an alternating 54/55/56 baseline)
+  // has no dispersion the sensor can actually resolve. Standardizing against
+  // it fabricates an extreme z off ordinary rounding noise — the same guard
+  // illness_cusum.dart and readiness_composite.dart already apply to this
+  // exact channel. Abstain on the RHR axis only; RMSSD isn't quantized this
+  // way, so it keeps standardizing normally.
+  final rhrBelowQuantum = dispersionBelowQuantum(rhrHistory, _rhrQuantum);
+  final rhrZ = rhrBelowQuantum ? null : rhrBase.modZ(tonight.rhr);
   final rmssdZ = rmsBase.modZ(tonight.rmssd);
 
   // MDC gates: a sign only counts if it clears the metric's minimal detectable
   // change. When MDC is unavailable (degenerate scale) the sign cannot fire.
-  final rhrMdc = mdc(rhrBase);
+  final rhrMdc = rhrBelowQuantum ? null : mdc(rhrBase);
   final rmsMdc = mdc(rmsBase);
   final rhrUp = rhrMdc != null && rhrDelta > rhrMdc;
   final rmssdDown = rmsMdc != null && (-rmssdDelta) > rmsMdc;
@@ -217,11 +232,14 @@ Metric<EventState> alcoholNightFlag(
       tonight.skinTempZ != null || tonight.respRate != null;
   final ambiguous = state == 'autonomically_stressed' && !hasDisambiguator;
 
-  final note = state == 'normal'
-      ? 'no autonomic signature tonight'
-      : 'STATE = autonomic stress (confident). "Alcohol" is a tag-confirmable '
-          'hypothesis only — late meal / early illness / luteal / hot room '
-          'share this signature; disambiguate with temp + respiration, not HR.';
+  final note = (state == 'normal'
+          ? 'no autonomic signature tonight'
+          : 'STATE = autonomic stress (confident). "Alcohol" is a tag-confirmable '
+              'hypothesis only — late meal / early illness / luteal / hot room '
+              'share this signature; disambiguate with temp + respiration, not HR.') +
+      (rhrBelowQuantum
+          ? '; rhr baseline dispersion below whole-bpm quantum — RHR axis abstained'
+          : '');
 
   return Metric<EventState>(
     value: EventState(
diff --git a/test/onehz/human_test.dart b/test/onehz/human_test.dart
index 617929f..e042ebd 100644
--- a/test/onehz/human_test.dart
+++ b/test/onehz/human_test.dart
@@ -107,8 +107,9 @@ void main() {
   });
 
   group('alcohol-night flag — fires at the right band, silent when normal', () {
-    // Personal baseline: RHR ~55 (tight), RMSSD ~60 (tight), dip ~12%, temp z ~0.
-    final rhrHist = [54.0, 55.0, 56.0, 55.0, 54.0, 55.0, 56.0, 55.0];
+    // Personal baseline: RHR ~55 (real dispersion, SD >= 1 whole-bpm quantum),
+    // RMSSD ~60 (tight), dip ~12%, temp z ~0.
+    final rhrHist = [52.0, 55.0, 58.0, 54.0, 56.0, 53.0, 57.0, 55.0];
     final rmsHist = [60.0, 61.0, 59.0, 60.0, 62.0, 58.0, 60.0, 61.0];
     final dipHist = [12.0, 11.5, 12.5, 12.0, 11.0, 13.0, 12.0, 12.0];
     final tempHist = [0.0, 0.1, -0.1, 0.0, 0.2, -0.2, 0.0, 0.1];
@@ -198,6 +199,30 @@ void main() {
       // other baseline-gated metric in this package uses.
       expect(m.note, 'need_baseline:have=2,need=7');
     });
+
+    test(
+        'sub-quantum RHR baseline: ordinary +3 bpm night does not fabricate '
+        'the alcohol signature', () {
+      // Whole-bpm-quantized baseline (SD ~0.76, below the 1 bpm quantum) —
+      // the exact shape illness_cusum.dart's guard was written for. An
+      // ordinary +3 bpm night must not standardize against rounding noise.
+      final quantizedRhrHist = [54.0, 55.0, 56.0, 55.0, 54.0, 55.0, 56.0, 55.0];
+      final tonight = NightSignature(
+        rhr: 58, // +3 bpm vs median 55 — unremarkable
+        rmssd: 60, // no RMSSD move at all
+        hrDipPct: 12,
+        skinTempZ: 0.0,
+      );
+      final m = alcoholNightFlag(tonight,
+          rhrHistory: quantizedRhrHist,
+          rmssdHistory: rmsHist,
+          hrDipHistory: dipHist,
+          skinTempZHistory: tempHist);
+      final v = m.value!;
+      expect(v.alcoholHypothesisBand, isNot(anyOf('moderate', 'heavy')));
+      expect(v.rhrZ, isNull);
+      expect(m.note, contains('rhr baseline dispersion below whole-bpm quantum'));
+    });
   });
 
   group('percentile-of-you + records (MDC-gated)', () {