How to spy on someone’s phone without them knowing for free?

If one wants to spy on someone’s phone without them knowing, they can do it by using spyware. This kind of application allows users to monitor someone’s device remotely anytime and delivers the data about its GPS location and the target person’s activity on it, such as the tracking of SMS, calls, imessages, web activity, installed applications, multimedia files, emails, etc. The most popular on the monitoring market are mSpy, Spyhuman, SpyBubble, Mobile Spy.