There are some signs that may let users to know that someone is monitoring their line. Some of these signs are: 1. You will be getting an unsuspicious text 2. You will discover that your device battery drains faster 3. Another way to know is that you will be seeing unwanted applications on your device 4. In order for the spy that is monitoring your line to achieve it, he or she uses global positioning system(GPS) which will in turn makes your device to overheats most times.