Firebase authentication when session expired

Question

I have an android app with firebase as database.I am using Firebase token for authentication.so.,the app session gets expired in each 1hr.so i want to logout and goto signin activity from home when token expired.How can i do it in my app.?

public class FragmentHome extends Fragment {
 private SearchView search;
 View v;
 DatabaseReference dataRef;
 private FirebaseListAdapter < String > firebaseListAdapter;
 ListView mListView;
 private TextView text;
 ArrayList < String > city = new ArrayList < String > ();
 private int i = 0;
 private String data, val,
 var;
 ArrayAdapter < String > adapter;
 ProgressBar progressBar;
 @Nullable @Override public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable final Bundle savedInstanceState) {
  v = inflater.inflate(R.layout.activity_fragment_home, container, false);
  if (container != null) {
   container.removeAllViews();
  }
  return v;
 }
 @Override public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
  super.onViewCreated(view, savedInstanceState);
  progressBar = (ProgressBar) v.findViewById(R.id.search_pro);
  search = (SearchView) v.findViewById(R.id.search);
  search.onActionViewExpanded();
  search.setIconified(false);
  search.setInputType(InputType.TYPE_NULL);
  search.setQueryHint("Search Docter By City Or Department");
  mListView = (ListView) v.findViewById(R.id.mList);
  mListView.setVisibility(View.INVISIBLE);
  dataRef = FirebaseDatabase.getInstance().getReference().child("Docters");
  adapter = new ArrayAdapter < String > (getActivity(), android.R.layout.simple_list_item_1, city);
  mListView.setAdapter(adapter);
  adapter.notifyDataSetChanged();
  dataRef.addChildEventListener(new ChildEventListener() {
   @Override public void onChildAdded(DataSnapshot dataSnapshot, String s) {
    data = dataSnapshot.child("city").getValue(String.class);
    val = dataSnapshot.child("department").getValue(String.class);
    if (!city.contains(data)) {
     city.add(data);
    }
    if (!city.contains(val)) {
     city.add(val);
    }
    search.setInputType(InputType.TYPE_CLASS_TEXT);
    progressBar.setVisibility(View.GONE);
    adapter.notifyDataSetChanged();
   }
   @Override public void onChildChanged(DataSnapshot dataSnapshot, String s) {
    data = dataSnapshot.child("city").getValue(String.class);
    val = dataSnapshot.child("department").getValue(String.class);
    city.add(data);
    city.add(val);
    city.add(var);
    adapter.notifyDataSetChanged();
   }
   @Override public void onChildRemoved(DataSnapshot dataSnapshot) {}
   @Override public void onChildMoved(DataSnapshot dataSnapshot, String s) {}
   @Override public void onCancelled(DatabaseError databaseError) {}
  });
  search.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
   @Override public boolean onQueryTextSubmit(String text) {
    return false;
   }
   @Override public boolean onQueryTextChange(String text) {
    if (!text.isEmpty()) {
     adapter.notifyDataSetChanged();
     mListView.setVisibility(View.VISIBLE);
     adapter.getFilter().filter(text);
    } else {
     mListView.setVisibility(View.INVISIBLE);
    }
    return false;
   }
  });
  mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
   @Override public void onItemClick(AdapterView < ? > parent, View view, int position, long id) {
    String itemRef = (String) adapter.getItem(position);
    search.setVisibility(View.INVISIBLE);
    mListView.setVisibility(View.INVISIBLE);
    FragmentTransaction ft = getChildFragmentManager().beginTransaction();
    DocterList fragment = new DocterList();
    Bundle item = new Bundle();
    item.putString("item", itemRef);
    fragment.setArguments(item);
    ft.replace(R.id.activity_fragment_home, fragment);
    ft.addToBackStack(null);
    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
    ft.commit();
   }
  });
 }