Is it possible for someone to install a spy app on an Android phone JB os? Do these spy apps really work? Can anyone install this spy app to your mobile phone without your knowledge? If you suspect that it's been installed to your mobile phone, how do you find it and uninstall it? Would it show as an installed app in your internal files accessible by apps like All-in-One Toolbox?
It is my understanding that, in a non-rooted android device at least, all apps are available to be seen by the user. Now unless there is a security vulnerability that I am unaware of a "spy-app" will be visible to the primary user and owner of the phone.
This does not mean it will be called "spy app" or anything that is obviously malicious but it does mean that if it is there then it will be visible.
A great way to check if an app could be a "spy app" is to check its permissions, other than that its just good practice to know what is on your phone (so you could see if an app is installed that you did not install).
In simple words YES! Can they be installed without your knowledge? Mostly no, but with hackers finding innovative ways to push malware through you could get affected.
Any app during installation asks for a few permissions, if I were to develop an application to spy on your location, your contacts, your messages etc I could very well just add these permissions on the app and discreetly upload your data. How would you prevent this? Well if you are downloading a music app and it asks your permission to send and receive messages or access your messages you can make an educated guess that something could be wrong here.
Your best bet at finding spy apps would be to see the permissions for apps downloaded and see if they match the functionality that is provided by them.