diff --git a/src/monitor.c b/src/monitor.c
new file mode 100644
index 0000000..c9607c1
--- /dev/null
+++ b/src/monitor.c
@@ -0,0 +1,22 @@
+#include "monitor.h"
+#include <string.h>
+
+void monitor_init(monitor_t *monitor) { if (monitor) memset(monitor, 0, sizeof(*monitor)); }
+
+frame_result_t monitor_accept(monitor_t *monitor, const uint8_t *bytes, size_t length) {
+    sample_t sample;
+    if (!monitor) return FRAME_SHORT;
+    frame_result_t result = decode_frame(bytes, length, &sample);
+    if (result != FRAME_OK) { monitor->rejected++; return result; }
+    if (monitor->has_last) {
+        uint16_t delta = (uint16_t)(sample.sequence - monitor->last_sequence);
+        if (delta == 0) { monitor->duplicate++; monitor->rejected++; return FRAME_DUPLICATE; }
+        if (delta > 32767) { monitor->rollback++; monitor->rejected++; return FRAME_ROLLBACK; }
+        if (delta > 1) monitor->lost += delta - 1;
+    }
+    monitor->accepted++;
+    monitor->last_sequence = sample.sequence;
+    monitor->last_sample = sample;
+    monitor->has_last = 1;
+    return FRAME_OK;
+}