diff --git a/src/model.mjs b/src/model.mjs
new file mode 100644
index 0000000..5cb9227
--- /dev/null
+++ b/src/model.mjs
@@ -0,0 +1,10 @@
+export const TYPES = new Set(['ALARM', 'ACK', 'CLEAR']);
+
+export function normalizeEvent(raw, index) {
+  if (!raw || !raw.device || !raw.alarmId || !TYPES.has(raw.type))
+    return { error: 'invalid event', index };
+  const time = Number(raw.time);
+  if (!Number.isFinite(time) || time < 0) return { error: 'invalid time', index };
+  return { device: String(raw.device), alarmId: String(raw.alarmId),
+    type: raw.type, time, index };
+}