diff --git a/heart_rate_sensor_protocol.h b/heart_rate_sensor_protocol.h
index 9b4c1ca..d59e100 100644
--- a/heart_rate_sensor_protocol.h
+++ b/heart_rate_sensor_protocol.h
@@ -12,15 +12,16 @@ typedef struct {
 } ify_hrs_packet_t;
 
 typedef enum {
-  kifyhrs_ecode_success           = 0,
-  kifyhrs_ecode_unkown_error      = 1,
-  kifyhrs_ecode_cmd_not_support   = 2,
-  kifyhrs_ecode_illegal_parameter = 3,
-  kifyhrs_ecode_device_busy       = 4,
-  kifyhrs_ecode_hardware_error    = 5,
-  kifyhrs_ecode_sensor_drop       = 6,
-  kifyhrs_ecode_no_record_find    = 7,
-  kifyhrs_ecode_parameter_error   = 8,
+  kifyhrs_ecode_success                   = 0,
+  kifyhrs_ecode_unkown_error              = 1,
+  kifyhrs_ecode_cmd_not_support           = 2,
+  kifyhrs_ecode_illegal_parameter         = 3,
+  kifyhrs_ecode_device_busy               = 4,
+  kifyhrs_ecode_hardware_error            = 5,
+  kifyhrs_ecode_sensor_drop               = 6,
+  kifyhrs_ecode_no_record_find            = 7,
+  kifyhrs_ecode_parameter_error           = 8,
+  kifyhrs_ecode_electrode_is_not_inserted = 9,
 } ify_hrs_error_code_t;
 
 typedef enum {