diff --git a/internal/alerts/quiet_hours_test.go b/internal/alerts/quiet_hours_test.go
index 133acd3..e56cecb 100644
--- a/internal/alerts/quiet_hours_test.go
+++ b/internal/alerts/quiet_hours_test.go
@@ -1,6 +1,9 @@
 package alerts
 
-import "testing"
+import (
+	"testing"
+	"time"
+)
 
 func newManagerWithQuietHoursSuppress(s QuietHoursSuppression) *Manager {
 	m := NewManager()
@@ -69,3 +72,204 @@ func TestShouldSuppressNotificationQuietHours(t *testing.T) {
 		}
 	})
 }
+
+func TestIsInQuietHours(t *testing.T) {
+	t.Parallel()
+
+	t.Run("disabled returns false", func(t *testing.T) {
+		t.Parallel()
+		m := NewManager()
+		m.mu.Lock()
+		m.config.Schedule.QuietHours.Enabled = false
+		m.mu.Unlock()
+
+		m.mu.RLock()
+		result := m.isInQuietHours()
+		m.mu.RUnlock()
+
+		if result {
+			t.Errorf("isInQuietHours() = true, want false when disabled")
+		}
+	})
+
+	t.Run("invalid timezone falls back to local", func(t *testing.T) {
+		t.Parallel()
+		m := NewManager()
+		m.mu.Lock()
+		m.config.Schedule.QuietHours = QuietHours{
+			Enabled:  true,
+			Start:    "00:00",
+			End:      "23:59",
+			Timezone: "Invalid/Timezone",
+			Days: map[string]bool{
+				"monday": true, "tuesday": true, "wednesday": true,
+				"thursday": true, "friday": true, "saturday": true, "sunday": true,
+			},
+		}
+		m.mu.Unlock()
+
+		// Should not panic, should fall back to local time
+		m.mu.RLock()
+		result := m.isInQuietHours()
+		m.mu.RUnlock()
+
+		// With all days enabled and 00:00-23:59, it should be true
+		if !result {
+			t.Errorf("isInQuietHours() = false, want true (invalid timezone should fall back to local)")
+		}
+	})
+
+	t.Run("day not enabled returns false", func(t *testing.T) {
+		t.Parallel()
+		m := NewManager()
+		now := time.Now()
+		currentDay := now.Format("Monday")
+
+		m.mu.Lock()
+		m.config.Schedule.QuietHours = QuietHours{
+			Enabled:  true,
+			Start:    "00:00",
+			End:      "23:59",
+			Timezone: "UTC",
+			Days:     map[string]bool{}, // No days enabled
+		}
+		m.mu.Unlock()
+
+		m.mu.RLock()
+		result := m.isInQuietHours()
+		m.mu.RUnlock()
+
+		if result {
+			t.Errorf("isInQuietHours() = true, want false (day %s not enabled)", currentDay)
+		}
+	})
+
+	t.Run("invalid start time returns false", func(t *testing.T) {
+		t.Parallel()
+		m := NewManager()
+
+		m.mu.Lock()
+		m.config.Schedule.QuietHours = QuietHours{
+			Enabled:  true,
+			Start:    "invalid",
+			End:      "23:59",
+			Timezone: "UTC",
+			Days: map[string]bool{
+				"monday": true, "tuesday": true, "wednesday": true,
+				"thursday": true, "friday": true, "saturday": true, "sunday": true,
+			},
+		}
+		m.mu.Unlock()
+
+		m.mu.RLock()
+		result := m.isInQuietHours()
+		m.mu.RUnlock()
+
+		if result {
+			t.Errorf("isInQuietHours() = true, want false (invalid start time)")
+		}
+	})
+
+	t.Run("invalid end time returns false", func(t *testing.T) {
+		t.Parallel()
+		m := NewManager()
+
+		m.mu.Lock()
+		m.config.Schedule.QuietHours = QuietHours{
+			Enabled:  true,
+			Start:    "00:00",
+			End:      "invalid",
+			Timezone: "UTC",
+			Days: map[string]bool{
+				"monday": true, "tuesday": true, "wednesday": true,
+				"thursday": true, "friday": true, "saturday": true, "sunday": true,
+			},
+		}
+		m.mu.Unlock()
+
+		m.mu.RLock()
+		result := m.isInQuietHours()
+		m.mu.RUnlock()
+
+		if result {
+			t.Errorf("isInQuietHours() = true, want false (invalid end time)")
+		}
+	})
+
+	t.Run("overnight quiet hours spanning midnight", func(t *testing.T) {
+		t.Parallel()
+		m := NewManager()
+
+		// Set up overnight quiet hours (22:00 to 06:00)
+		m.mu.Lock()
+		m.config.Schedule.QuietHours = QuietHours{
+			Enabled:  true,
+			Start:    "22:00",
+			End:      "06:00", // End before start = overnight
+			Timezone: "UTC",
+			Days: map[string]bool{
+				"monday": true, "tuesday": true, "wednesday": true,
+				"thursday": true, "friday": true, "saturday": true, "sunday": true,
+			},
+		}
+		m.mu.Unlock()
+
+		// This tests the overnight branch - exact result depends on current time
+		// but should not panic
+		m.mu.RLock()
+		_ = m.isInQuietHours()
+		m.mu.RUnlock()
+	})
+
+	t.Run("normal daytime quiet hours", func(t *testing.T) {
+		t.Parallel()
+		m := NewManager()
+
+		// Set up daytime quiet hours (09:00 to 17:00)
+		m.mu.Lock()
+		m.config.Schedule.QuietHours = QuietHours{
+			Enabled:  true,
+			Start:    "09:00",
+			End:      "17:00",
+			Timezone: "UTC",
+			Days: map[string]bool{
+				"monday": true, "tuesday": true, "wednesday": true,
+				"thursday": true, "friday": true, "saturday": true, "sunday": true,
+			},
+		}
+		m.mu.Unlock()
+
+		// Should not panic, result depends on current time
+		m.mu.RLock()
+		_ = m.isInQuietHours()
+		m.mu.RUnlock()
+	})
+
+	t.Run("outside quiet hours window", func(t *testing.T) {
+		t.Parallel()
+		m := NewManager()
+
+		// Use a time window that's definitely not now (narrow window in far past/future time)
+		// This creates a window from 03:00-03:01 which is unlikely to match current time
+		m.mu.Lock()
+		m.config.Schedule.QuietHours = QuietHours{
+			Enabled:  true,
+			Start:    "03:00",
+			End:      "03:01", // 1 minute window
+			Timezone: "UTC",
+			Days: map[string]bool{
+				"monday": true, "tuesday": true, "wednesday": true,
+				"thursday": true, "friday": true, "saturday": true, "sunday": true,
+			},
+		}
+		m.mu.Unlock()
+
+		m.mu.RLock()
+		result := m.isInQuietHours()
+		m.mu.RUnlock()
+
+		// Very narrow window, likely false but depends on exact test execution time
+		// Main purpose is to exercise the "outside window" return false path
+		_ = result
+	})
+}