Flutter - Activity Tracker App - Steps, Upstairs/downstairs, Stationary

I would like to use Flutter to create an app that tracks the user's current activity state - whether they are going up or down stairs, or if they are walking or stationary. The reason why I am using Flutter is because it needs to be integrated to an existing Flutter app, managed by another team.

I am new to software development. I would like to use the phone sensors: gyroscope, accelerometer and barometer. May I know where to start? E.g. useful packages and APIs, platform channels?

You can use package https://pub.dev/packages/sensors
example code https://github.com/flutter/plugins/blob/master/packages/sensors/example/lib/main.dart

code snippet

@override
  Widget build(BuildContext context) {
    final List<String> accelerometer =
        _accelerometerValues?.map((double v) => v.toStringAsFixed(1))?.toList();
    final List<String> gyroscope =
        _gyroscopeValues?.map((double v) => v.toStringAsFixed(1))?.toList();
    final List<String> userAccelerometer = _userAccelerometerValues
        ?.map((double v) => v.toStringAsFixed(1))
        ?.toList();

@override
  void initState() {
    super.initState();
    _streamSubscriptions
        .add(accelerometerEvents.listen((AccelerometerEvent event) {
      setState(() {
        _accelerometerValues = <double>[event.x, event.y, event.z];
      });
    }));
    _streamSubscriptions.add(gyroscopeEvents.listen((GyroscopeEvent event) {
      setState(() {
        _gyroscopeValues = <double>[event.x, event.y, event.z];
      });
    }));
    _streamSubscriptions
        .add(userAccelerometerEvents.listen((UserAccelerometerEvent event) {
      setState(() {
        _userAccelerometerValues = <double>[event.x, event.y, event.z];
      });
    }));
  }