Here are some of the suspected signs that might help one determine if there are any possible chances of them being monitored
a. Battery drain away faster
If you start noticing that your battery charge is going down much faster than ever before, there is a strong possibility that someone might be keeping an eye on you. Undoubtedly, the battery quality of the phone demises with time and after a few years, but such effects are not visible instantly.
If the battery capacity and performance change drastically in a few days, especially when one is not using the phone, something might be wrong. The spyware apps utilize the camera, microphone, and other additional applications to send data which leads to fast battery drainage. If you are facing such a situation, consider getting the cell phone checked for the spyware or install some applications for the safeguard.
b. Increased data usage
Increased data usage even when you have been spending less time or no time online can be due to few factors, recently installed application that runs in the background, some malware or spy apps. In order to detect the chances of spyware installed in the phone one must know how much data they regularly use monthly and look at the data usage pattern to get a clear picture. There are plenty of applications available which helps one manage and track the data usage both on mobile data and Wi-Fi.
There could be some additional signs or changes in phone functionalities including cryptic text messages, unusual signs etc. that must not be ignored to ensure the security of your smartphone and stored information.