Many minor improvements

lib/models/device_status.dart

@@ -0,0 +1,16 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'device_status.g.dart';
+
+@JsonSerializable()
+class DeviceStatus {
+  bool entryNfc = false;
+  bool exitNfc = false;
+
+  DeviceStatus({this.entryNfc = false, this.exitNfc = false});
+
+  factory DeviceStatus.fromJson(Map<String, dynamic> json) =>
+      _$DeviceStatusFromJson(json);
+
+  Map<String, dynamic> toJson() => _$DeviceStatusToJson(this);
+}