Nothing technical is involved and nobody is breaking in. People are found out through autocomplete and lock-screen previews, so the cures are simple, about ten minutes of work all told.
Eight ways it gets out
Address-bar suggestions. Two keystrokes and the browser offers the site. This is the most common slip by a wide margin, and deleting your history does not cure it when the site is bookmarked or has a stored login.
Lock-screen alerts. These can be from the app itself or from your bank about the charge. A preview shows the sender and first line to everyone in the room.
Synced tabs and history. Chrome, Safari and Firefox share data across devices on one account, so a tab open on your laptop may appear on a family iPad logged in to it. Private browsing offers no defence, because that tab sat in your ordinary profile and was never private.
Saved passwords. Autofill keeps a list of the sites you use, which anyone with an unlocked device can read.
The Downloads folder. Generated images land in it with descriptive file names.
Photo sync. A picture saved on a phone can travel into a photo library that backs up to a shared family album.
App store purchase records. Under Family Sharing, other members can see your purchases.
Keyboard learning. A phone keyboard remembers what you type and suggests it elsewhere, including in messaging apps. Many people are startled by this one.
Remedies, best first
Set up a separate browser profile
If you do only one thing, do this; it needs around two minutes. Add a second profile in Chrome or Firefox, either signed out or linked to a different account, and it gets its own history, suggestions, stored logins and sync.
That alone handles autocomplete, sync, passwords and most of what remains. Since it keeps you logged in, unlike private browsing, it is a habit you can sustain.
Switch off notification previews
The easiest approach is to change it device-wide. On an iPhone, open Settings → Notifications → Show Previews and choose When Unlocked; Android offers the same in its notification settings. Apply it to your bank's app as well, for the reasons covered in payment privacy.
Skip saving the password on the shared profile
Keep it in a password manager that has its own lock, not in browser autofill on a device other people touch.
Move the download location
Send image downloads somewhere other than the default folder, and pick a location that does not sync.
Reset keyboard learning
On iOS, Reset Keyboard Dictionary clears what the keyboard has learned. On Android, check the keyboard's personalization options. Doing this once, a few weeks in, is worthwhile.
Why private browsing falls short
Precision matters here, because many people lean on it and it addresses only part of the problem.
Private mode keeps history, cookies and cached files from persisting on the device. It does not block synced tabs, saved passwords, downloads, alerts, keyboard learning or anything visible on the network. It also logs you out after each session, which for a web-only app means signing in repeatedly.
A separate profile accomplishes more with less friction.
Why a web-only app can be the safer pick
Camsoda AI and Joi work only in a browser, as does Secret Desires on mobile. On a phone that others use this is a real plus: no icon, nothing in the app switcher, no line in the purchase history.
The catch is short-lived sessions. Browsers wipe cookies and iOS readily discards site data, so you will log in often. Browser or app store sets out the full comparison.
If the device belongs to someone else
A work laptop is another matter altogether. Assume the network is monitored, that software on a managed device can see browsing even in private mode, and that IT can read it. No browser setting changes this.
The only right answer on employer equipment is to stay away. That is advice about your job, not about privacy.
What this cannot do
None of it shields you from a person who has your unlocked device and wants to look. It guards against the accidental case, meaning a glance at a lock screen, a shared tab or an autocomplete suggestion, which is what happens in practice.
Combine it with the account-side steps in account security and the realistic risks are covered.
