How to spy on a cell phone without installing software?

At present, any phone user can spy on another cell phone. It is possible due to spyware. However, the promise of doing it without software seems unfeasible. Here’s why.
For Android devices, the installation is a must because software must be present on the device to record its activities. For iOS ones, the installation is performed differently – by enabling the iCloud backup and learning Apple ID of the target device. The very next step for iOS handsets is to add it to the spyware service’s account by indicating Apple ID. Thus, in both cases, the installation is a must. However, the good news is that once spyware is installed, there’s no need to take it anymore to spy on it. The monitoring happens online from an online account given to a user by the service.