How to prevent Android from auto signing in to gmail, hangouts etc?

I just got an Android phone. To be able to download apps, I need to sign-in to Google Play with gmail account. I did.

But now gmail, hangouts, maps, drive etc. are all automatically configured with this gmail account.

I want to sign-in to google play account with my google-account but I dont want gmail, hangout, drive to automatically work/sign-in to the said gmail account.

I found sync settings where you can uncheck which apps can synch with google account. But it seems like if (my phone is unlocked), anyone can pick-up the phone, check those sync settings and gmail, hangout etc would start working!

I have a Nexus 5 running Lollipop.