diff --git a/gdata-characteristic.js b/gdata-characteristic.js
index 2fcd438..c75a73e 100644
--- a/gdata-characteristic.js
+++ b/gdata-characteristic.js
@@ -4,6 +4,7 @@ const localEvent = require('./localEvent')
 
 var tmp = []
 var idx = 0
+var failFlag = false
 
 const notifyDesciptor = new bleno.Descriptor({
   uuid: '8888',
@@ -29,12 +30,23 @@ class DataCharacteristic extends bleno.Characteristic {
     if (data.length == 1 && data[0] == 0x00) {
       tmp = []
       idx = 0
+      failFlag = false
     } else if (data.length == 1 && data[0] == 0xff) {
       console.log(Buffer.from(tmp).toString())
-      localEvent.emit('print', Buffer.from(tmp).toString())
-    } else {
+      if (!failFlag) {
+        localEvent.emit('print', Buffer.from(tmp).toString())
+      }
+    } else if (!failFlag) {
+      let pidx = ((data[0] & 0xff) << 8) + (data[1] & 0xff)
+      if (idx !== pidx) {
+        // insert fail method
+        failFlag = true
+        this.sendNotidy('fail')
+      }
+      idx++
       tmp = [...tmp, ...data.slice(2, data.length)]
     }
+
     if (!withoutResponse) {
       console.log('send response')
       callback(this.RESULT_SUCCESS)