diff --git a/src/polymarket_insider_tracker/detector/size_anomaly.py b/src/polymarket_insider_tracker/detector/size_anomaly.py
index b348dee..151e58e 100644
--- a/src/polymarket_insider_tracker/detector/size_anomaly.py
+++ b/src/polymarket_insider_tracker/detector/size_anomaly.py
@@ -17,6 +17,9 @@ logger = logging.getLogger(__name__)
 DEFAULT_VOLUME_THRESHOLD = 0.02  # 2% of daily volume
 DEFAULT_BOOK_THRESHOLD = 0.05  # 5% of order book depth
 DEFAULT_NICHE_VOLUME_THRESHOLD = Decimal("50000")  # $50k daily volume
+# Niche-only path requires real trade size; below this, suppress the base
+# 0.2 confidence so we don't flood alerts with low-value niche trades.
+DEFAULT_NICHE_MIN_TRADE_SIZE = Decimal("500")  # USDC notional
 
 # Niche market categories - markets in these categories with low specificity
 # are more likely to have insider information value
@@ -59,6 +62,7 @@ class SizeAnomalyDetector:
         volume_threshold: float = DEFAULT_VOLUME_THRESHOLD,
         book_threshold: float = DEFAULT_BOOK_THRESHOLD,
         niche_volume_threshold: Decimal = DEFAULT_NICHE_VOLUME_THRESHOLD,
+        niche_min_trade_size: Decimal = DEFAULT_NICHE_MIN_TRADE_SIZE,
     ) -> None:
         """Initialize the size anomaly detector.
 
@@ -67,11 +71,15 @@ class SizeAnomalyDetector:
             volume_threshold: Threshold for volume impact (default 0.02 = 2%).
             book_threshold: Threshold for book impact (default 0.05 = 5%).
             niche_volume_threshold: Volume below which market is niche ($50k).
+            niche_min_trade_size: Minimum trade notional ($) to allow a
+                niche-only signal. Below this, niche-only path is suppressed
+                to avoid flooding alerts with low-value trades.
         """
         self._metadata_sync = metadata_sync
         self._volume_threshold = volume_threshold
         self._book_threshold = book_threshold
         self._niche_volume_threshold = niche_volume_threshold
+        self._niche_min_trade_size = niche_min_trade_size
 
     async def analyze(
         self,
@@ -129,6 +137,18 @@ class SizeAnomalyDetector:
         exceeds_volume = volume_impact > self._volume_threshold
         exceeds_book = book_impact > self._book_threshold
 
+        # Niche-only signals require a minimum trade size; otherwise we'd
+        # flood alerts with every tiny trade in any niche-prone category.
+        niche_only = is_niche and not exceeds_volume and not exceeds_book
+        if niche_only and trade_size < self._niche_min_trade_size:
+            logger.debug(
+                "Trade %s niche-only but size %s < min %s, skipping",
+                trade.trade_id,
+                trade_size,
+                self._niche_min_trade_size,
+            )
+            return None
+
         if not exceeds_volume and not exceeds_book and not is_niche:
             logger.debug(
                 "Trade %s does not exceed thresholds: volume=%.4f, book=%.4f",
diff --git a/tests/detector/test_size_anomaly.py b/tests/detector/test_size_anomaly.py
index f214c01..963c917 100644
--- a/tests/detector/test_size_anomaly.py
+++ b/tests/detector/test_size_anomaly.py
@@ -588,6 +588,93 @@ class TestAnalyzeMethod:
         assert signal.is_niche_market is True
         assert signal.confidence == 0.2  # niche_base
 
+    @pytest.mark.asyncio
+    async def test_analyze_niche_only_below_min_trade_size_skipped(
+        self,
+        mock_metadata_sync: AsyncMock,
+        sample_metadata: MarketMetadata,
+    ) -> None:
+        """Niche-only trades below the min trade size are suppressed."""
+        mock_metadata_sync.get_market.return_value = sample_metadata
+        detector = SizeAnomalyDetector(mock_metadata_sync)
+
+        tiny_trade = TradeEvent(
+            market_id="market_abc123",
+            trade_id="tx_tiny",
+            wallet_address="0xabc",
+            side="BUY",
+            outcome="Yes",
+            outcome_index=0,
+            price=Decimal("0.5"),
+            size=Decimal("100"),  # $50 notional, below default $500 floor
+            timestamp=datetime.now(UTC),
+            asset_id="token_123",
+            event_title="Niche tiny trade",
+        )
+
+        signal = await detector.analyze(tiny_trade)
+        assert signal is None
+
+    @pytest.mark.asyncio
+    async def test_analyze_niche_only_at_min_trade_size_emits(
+        self,
+        mock_metadata_sync: AsyncMock,
+        sample_metadata: MarketMetadata,
+    ) -> None:
+        """Niche-only trades at or above the min trade size still emit."""
+        mock_metadata_sync.get_market.return_value = sample_metadata
+        detector = SizeAnomalyDetector(mock_metadata_sync)
+
+        ok_trade = TradeEvent(
+            market_id="market_abc123",
+            trade_id="tx_ok",
+            wallet_address="0xabc",
+            side="BUY",
+            outcome="Yes",
+            outcome_index=0,
+            price=Decimal("0.5"),
+            size=Decimal("2000"),  # $1000 notional, above default $500 floor
+            timestamp=datetime.now(UTC),
+            asset_id="token_123",
+            event_title="Niche ok trade",
+        )
+
+        signal = await detector.analyze(ok_trade)
+        assert signal is not None
+        assert signal.is_niche_market is True
+        assert signal.confidence == 0.2
+
+    @pytest.mark.asyncio
+    async def test_niche_min_trade_size_does_not_block_real_anomalies(
+        self,
+        mock_metadata_sync: AsyncMock,
+        sample_metadata: MarketMetadata,
+    ) -> None:
+        """A trade that exceeds volume/book thresholds is never blocked by the niche guard."""
+        mock_metadata_sync.get_market.return_value = sample_metadata
+        detector = SizeAnomalyDetector(mock_metadata_sync)
+
+        small_but_high_impact_trade = TradeEvent(
+            market_id="market_abc123",
+            trade_id="tx_small_impact",
+            wallet_address="0xabc",
+            side="BUY",
+            outcome="Yes",
+            outcome_index=0,
+            price=Decimal("0.5"),
+            size=Decimal("200"),  # $100 notional, below niche floor
+            timestamp=datetime.now(UTC),
+            asset_id="token_123",
+            event_title="Small but high-impact",
+        )
+
+        # Provide small daily_volume so volume_impact exceeds 2% threshold
+        signal = await detector.analyze(
+            small_but_high_impact_trade, daily_volume=Decimal("1000")
+        )
+        assert signal is not None
+        assert signal.volume_impact > 0.02
+
     @pytest.mark.asyncio
     async def test_analyze_no_anomaly(
         self,