The app Is designed to run in background.. You enter a phone number for a SMS, and it will send a message immediately back to that sms when a text is received... NOW it does not actually block the sms.. but in my case it sends a text saying it did.. This was done so ex girlfriend would THINK her text's were being blocked.. Yes I could have used the samsungs a71 sms spam filter, but then she would not receive a message, and think I was getting her text's... If you can improve this let me know..