diff --git a/main.go b/main.go
index 42edb07..6646998 100644
--- a/main.go
+++ b/main.go
@@ -205,7 +205,7 @@ func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string,
 	now := t0
 
 	if r < d.rmsThresh {
-		slog.Debug("Window at %s: RMS %.2f below threshold %.2f, resetting", now.Format(time.RFC3339), r, d.rmsThresh)
+		slog.Debug("Window RMS below threshold, resetting", "at", now.Format(time.RFC3339), "RMS", r, "threshold", d.rmsThresh)
 		d.reset()
 		return "", 0, 0, 0, 0
 	}
@@ -222,7 +222,7 @@ func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string,
 	}
 	ratio := bestPow / (total + 1e-12)
 	if ratio < d.ratioThresh {
-		slog.Debug("Window at %s: ratio %.3f below threshold %.3f, resetting", now.Format(time.RFC3339), ratio, d.ratioThresh)
+		slog.Debug("Window ratio below threshold, resetting", "at", now.Format(time.RFC3339), "ratio", ratio, "threshold", d.ratioThresh)
 		d.reset()
 		return "", 0, 0, 0, 0
 	}
@@ -244,7 +244,7 @@ func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string,
 				d.gapRemainMs = d.gapMaxMs
 			}
 		} else {
-			slog.Debug("Window at %s: freq %.1f Hz differs from Tone A %.1f Hz, resetting", now.Format(time.RFC3339), freq, d.aFreq)
+			slog.Debug("Window freq differs from Tone A, resetting A", "at", now.Format(time.RFC3339), "freq (Hz)", freq, "Tone A (Hz)", d.aFreq)
 			d.reset()
 		}
 	} else if d.waitingB {
@@ -258,7 +258,7 @@ func (d *twoToneDetector) stepWindow(pcms []int16, t0 time.Time) (event string,
 				d.bFreq = freq
 				d.bStart = now
 			} else if math.Abs(freq-d.bFreq) > 10.0 {
-				slog.Debug("Window at %s: freq %.1f Hz differs from Tone B %.1f Hz, resetting B", now.Format(time.RFC3339), freq, d.bFreq)
+				slog.Debug("Window freq differs from Tone B, resetting B", "at", now.Format(time.RFC3339), "freq (Hz)", freq, "Tone B (Hz)", d.bFreq)
 				d.bFreq = freq
 				d.bAccumMs = 0
 				d.bStart = now
@@ -426,8 +426,7 @@ func main() {
 			if det.recording {
 				if !det.bEnd.IsZero() && !chunkTime.Before(det.bEnd.Add(100*time.Millisecond)) {
 					r := rmsPCM(chunk)
-					slog.Info("Chunk at %s: RMS=%.2f, silenceThresh=%.2f, silenceAccum=%d ms, recordBuf=%d samples",
-						chunkTime.Format(time.RFC3339), r, *silenceThresh, det.silenceAccumMs, len(det.recordBuf))
+					slog.Info("chunk", "at", chunkTime.Format(time.RFC3339), "RMS", r, "silenceThresh", *silenceThresh, "silenceAccum (ms)", det.silenceAccumMs, "record buffer (samples)", len(det.recordBuf))
 					if r < *silenceThresh {
 						det.silenceAccumMs += int(time.Duration(len(chunk)) * time.Second / time.Duration(fs) / time.Millisecond)
 						if det.silenceAccumMs >= *silenceDurMs && len(det.recordBuf) > 0 {
diff --git a/main_test.go b/main_test.go
new file mode 100644
index 0000000..4c5df5b
--- /dev/null
+++ b/main_test.go
@@ -0,0 +1,100 @@
+package main
+
+import (
+	"math"
+	"testing"
+	"time"
+)
+
+// Test decodeMuLaw basic functionality
+func TestDecodeMuLaw(t *testing.T) {
+	data := []byte{0x00, 0xFF, 0x7F, 0x80}
+	pcm, err := decodeMuLaw(data)
+	if err != nil {
+		t.Fatalf("decodeMuLaw returned error: %v", err)
+	}
+	if len(pcm) != len(data) {
+		t.Errorf("Expected %d samples, got %d", len(data), len(pcm))
+	}
+}
+
+// Test Goertzel power calculation
+func TestGoertzelPower(t *testing.T) {
+	fs := 8000.0
+	N := 100
+	freq := 1000.0
+	g := newGoertzel(freq, fs, N)
+	signal := make([]float64, N)
+	for i := range signal {
+		signal[i] = math.Sin(2 * math.Pi * freq * float64(i) / fs)
+	}
+	power := g.Power(signal)
+	if power <= 0 {
+		t.Errorf("Expected positive power, got %f", power)
+	}
+}
+
+// Test windowHann modifies slice
+func TestWindowHann(t *testing.T) {
+	x := []float64{1, 1, 1, 1}
+	windowHann(x)
+	for i, v := range x {
+		if v == 1 {
+			t.Errorf("windowHann did not modify value at index %d", i)
+		}
+	}
+}
+
+// Test rmsPCM returns correct RMS
+func TestRmsPCM(t *testing.T) {
+	buf := []int16{1000, -1000, 1000, -1000}
+	rms := rmsPCM(buf)
+	if rms < 900 || rms > 1100 {
+		t.Errorf("Unexpected RMS value: %f", rms)
+	}
+}
+
+// Test twoToneDetector reset
+func TestTwoToneDetectorReset(t *testing.T) {
+	d := newTwoToneDetector(8000, 100, 50, 0.65, 300, 1000, 3000, 5000)
+	d.inA = true
+	d.aFreq = 1000
+	d.reset()
+	if d.inA || d.aFreq != 0 {
+		t.Errorf("reset did not clear state")
+	}
+}
+
+// Test min function
+func TestMin(t *testing.T) {
+	if min(1, 2) != 1 {
+		t.Errorf("min(1,2) should be 1")
+	}
+	if min(2, 1) != 1 {
+		t.Errorf("min(2,1) should be 1")
+	}
+	if min(2, 2) != 2 {
+		t.Errorf("min(2,2) should be 2")
+	}
+}
+
+// Test saveToWAV (does not check file output, just runs function)
+func TestSaveToWAV(t *testing.T) {
+	data := make([]int16, 8000)
+	for i := range data {
+		data[i] = int16(i % 32768)
+	}
+	saveToWAV(data, 8000)
+	// No assertion, just ensure no panic
+}
+
+// Test stepWindow returns expected values for silence
+func TestStepWindowSilence(t *testing.T) {
+	d := newTwoToneDetector(8000, 100, 50, 0.65, 300, 1000, 3000, 5000)
+	buf := make([]int16, 100)
+	t0 := time.Now()
+	event, aFreq, aDur, bFreq, bDur := d.stepWindow(buf, t0)
+	if event != "" || aFreq != 0 || aDur != 0 || bFreq != 0 || bDur != 0 {
+		t.Errorf("stepWindow should return zero values for silence")
+	}
+}