FirebaseDatabase database = FirebaseDatabase.getInstance();
databaseReference = database.getReference("open");
databaseReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        setDoorBtnState(!dataSnapshot.getValue(boolean.class));
    }
}
Screen Shot 2018-06-14 at 13.58.29.png