If you are worried that someone in your family or household might snoop around your journal it's hard to relax and write freely.
Complete privacy to write whatever you want without worrying about what others think is one of the most important requirements for a journaler. Of course, sometimes you may want to share some highlight or light bulb moment, but it must be of your own choosing, not stolen from you.
With very sensitive or hurtful writing you might choose to write on scrap paper and then destroy it. Ceremoniously burning it afterward might be satisfying!
Otherwise write in your journal in code or more illegibly than usual.
It's great if you trust your family to leave your private musings alone or have a hiding place for them, but there are few other options for a handwritten journal.
Computer or app journals come into their own in this situation.
Day One for Mac and iOS users
Diarium for Windows users
Penzu especially if you want very a secure journal
Journey works on all platforms
Reflection.app also works on all platforms and is secure
Once you have acquired a library of journals, as I have, it would be a good idea to give a trusted friend or family member instructions on how to deal with it if something happens to you. I know someone who has left a note in his will with instructions to destroy all of his journals.