diff --git a/app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PiezoMonitoringView.kt b/app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PiezoMonitoringView.kt
index 8783e7e..38edc70 100644
--- a/app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PiezoMonitoringView.kt
+++ b/app/src/main/java/com/example/medilightv2android/ui/views/monitoring/PiezoMonitoringView.kt
@@ -120,25 +120,39 @@ fun PiezoMonitoringView(appState: AppState) {
                         }
                     }
 
-                    // 6ch BV estimation (center 4ch + lateral lr_ratio)
-                    val bvResult = estimateBladderVolume6ch(allWalls)
-                    if (bvResult != null) {
-                        lastVolumeMl = bvResult.volumeMl
-                        maxVolumeMl = maxOf(maxVolumeMl, bvResult.volumeMl)
-                        Log.d("PiezoMonitor", "BV: ${"%.1f".format(bvResult.volumeMl)}ml (6ch, lr=${
-                            "%.2f".format(bvResult.lrRatio)}, ${bvResult.validChannels.size}ch)")
-                    } else {
-                        Log.d("PiezoMonitor", "BV: estimation failed (< 2 valid channels)")
-                    }
+                    // Count valid center channels (CH0~CH3)
+                    val centerWallCount = (0..3).count { allWalls[it] != null }
+                    val totalWallCount = allWalls.count { it != null }
 
-                    // Log per-channel detail
                     for (ch in analysisResult.channels) {
                         if (ch.isValid && ch.result != null) {
                             Log.d("PiezoMonitor", "  CH${ch.channel}: ant=${ch.result.ant} post=${ch.result.post} urine=${ch.result.urineLen} score=${"%.1f".format(ch.result.score)}")
                         }
                     }
+
+                    if (centerWallCount >= 3) {
+                        // 6ch BV estimation (center 4ch + lateral lr_ratio)
+                        val bvResult = estimateBladderVolume6ch(allWalls)
+                        if (bvResult != null) {
+                            lastVolumeMl = bvResult.volumeMl
+                            maxVolumeMl = maxOf(maxVolumeMl, bvResult.volumeMl)
+                            Log.d("PiezoMonitor", "BV: ${"%.1f".format(bvResult.volumeMl)}ml (6ch, lr=${"%.2f".format(bvResult.lrRatio)}, center=${centerWallCount}/4)")
+                            bleManager.debugLogger.measurementResult(bvResult.volumeMl, bvResult.lrRatio, totalWallCount,
+                                (0..5).map { allWalls[it]?.let { w -> w.second - w.first } ?: 0 })
+                        }
+                    } else if (centerWallCount > 0) {
+                        Log.w("PiezoMonitor", "Insufficient center channels: $centerWallCount/4 (need 3+)")
+                        bleManager.debugLogger.warn("BV_SKIP center=$centerWallCount/4 total=$totalWallCount/6")
+                        android.widget.Toast.makeText(context,
+                            "측정 부족 (${centerWallCount}/4채널) — 센서 위치를 조절해주세요",
+                            android.widget.Toast.LENGTH_SHORT).show()
+                    }
                 } else {
                     Log.d("PiezoMonitor", "No valid channels — volume unchanged")
+                    bleManager.debugLogger.warn("BV_FAIL no valid channels")
+                    android.widget.Toast.makeText(context,
+                        "방광이 감지되지 않았습니다. 센서 접촉을 확인해주세요.",
+                        android.widget.Toast.LENGTH_SHORT).show()
                 }
 
                 // Update level based on measured volume