How to spy on a cell phone without software installation?

To spy on a cell phone without software installation depends on the type of information one needs. Most online services allow spying on the GPS location of the target device. For example, Google has Find My Phone that tracks associated Android phones.
Mobile providers, such as AT&T or Verizon, are service-based and allow tracking their phones within their programs. Also, it’s possible to track text messages.
Phone manufacturers claim to find phones by IMEI numbers. But this way is not resultful. In a nutshell, to spy on a cell phone without software installation means spying on GPS location. To get to know much more about people needs spyware and their installation on the target device.