How do I keep my privacy on a shared or family laptop?
Give everyone their own Windows account, and make sure yours has a password and is the only administrator account you use. Turn on device encryption, keep your files inside your own account, and sign out of browsers and apps rather than just closing them. When you lend the laptop, sign them in to a separate or guest account instead of handing over yours. If you want to know what happened while someone else used it, keep a record, and tell them it is on: recording another person without telling them is not fair, and in many places not lawful.
Accounts are the real boundary
On Windows, each account has its own Documents, Pictures, Desktop and browser profile. Another standard account cannot open them without an administrator's help. Most of the privacy problems on shared computers come from everyone using one account, where every file and every signed in site is open to whoever sits down.
An administrator account can reach everything, so the fewer people who have one, the better. Device encryption protects the drive if the laptop is lost or its drive is removed; it does not protect files from someone using the laptop while it is signed in.
When you lend it for an afternoon
Sign them in to their own account, or create a temporary one and delete it afterwards. Close and sign out of your email, bank and social media first. Removable drives are the easiest way for files to leave, so notice whether anything was plugged in.
Being fair to the people you share with
Keeping a record of what happens on your own computer is reasonable. Using it to watch a partner, a housemate or a family member secretly is not. Tell the people who use the computer that a record is kept. It is the right thing to do, and it also means the record is useful rather than a source of conflict.
Rashnova's always on recording is built for this situation. It is off until you turn it on, and it keeps the irreversible and the alarming: a drive being plugged in, files copied to it, permanent deletions, files that look like passwords or tax papers. It does not keep your ordinary use of your own files. The app asks before it starts and reminds you to tell other people who use the computer. It is free and keeps everything on the laptop.