final Button checkButton = (Button) findViewById(R.id.checkBtn);
        checkButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                mDatabase.child("users").child(mUserId).child("barcodes").orderByChild("content")
                        .equalTo(contentTxt.toString()).addListenerForSingleValueEvent(new ValueEventListener(){
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        if (dataSnapshot.hasChildren()){
                            // method that alters update text TextBox
                            set_alarm_text("Alarm off!");

                            // cancel the alarm
                            alarm_manager.cancel(pending_intent);

                            // put in extra string into my_intent, telling the clock that "Alarm Off" was pressed
                            my_intent.putExtra("extra", "alarm off");

                            // stop the ringtone
                            sendBroadcast(my_intent);
                        }
                        else{
                            Toast toast = Toast.makeText(getApplicationContext(),
                                    "This is not a scanned barcode!", Toast.LENGTH_SHORT);
                            toast.show();
                        }
                    }
                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
            }
        });