1. The battery has a high temperature
When your phone's battery is very hot, it is actively discharging. This phenomenon is normal during a call, but when the phone is inactive and the battery is still very hot, it means that certain functions are going on inside the phone, for example, spyware is running.
2. The phone is discharging too quickly
Most often this happens because of a dangerous application in your phone. But this point can only be considered if you have a new battery, as batteries wear out over time and the fact that it has become less able to hold a charge is normal.
3. Delay in turning off.
If this process takes just a suspicious amount of time, plus you for some reason during this action begins to flash the backlight, it is likely that you are being bugged. Of course, this can be a problem with the phone, but other options should not be excluded.
4. Pickups and disturbances
You can hear yourself being bugged. Interference that occurs when it shouldn't. Different hisses and clicks during each conversation.
If you find signs of eavesdropping, don't panic. First, have your phone checked by the service. If there is nothing wrong with it, then you are being bugged.