Undetectable?
Nope. There is no such thing as undetectable. Cheat engine utilizes simply memory addresses and manipulates the address locations that the games read from by injecting the process directly onto it. One small minor mistake and the server can check via log, variation of security checksums etc.
The only way to be undetectable is experience, knowing the basics such as understanding how memory is called from and stored to an address location etc. all in order to avoid very amateur mistakes.