The Stealth Data Drain
If you own both a Mac and an iPhone signed into the same Apple ID, macOS features deep integration known as Continuity. Part of this integration includes the ability to automatically detect and connect to your iPhone’s Personal Hotspot if your Mac loses its primary Wi-Fi connection. While this is a lifesaver if your home internet goes down during an important Zoom call, it can be a financial disaster if you are on a limited cellular data plan. If your Mac briefly drops its connection to a flaky coffee shop Wi-Fi network, it might instantly and silently tether to your phone in your pocket, burning through gigabytes of cellular data for background updates before you even realize what has happened.
Disabling Automatic Tethering
To protect your cellular data cap and stop macOS from automatically connecting to your iPhone’s Personal Hotspot without explicit permission, you must adjust the Wi-Fi network preferences.
Click the Apple logo in the top-left corner of the screen and select System Settings. In the left-hand sidebar, click on Wi-Fi. In the main Wi-Fi panel, look down below the list of “Known Networks” and find the section regarding Hotspots. Look for a setting labelled Ask to join hotspots (this wording can vary slightly depending on your exact macOS version, sometimes located under an “Advanced” or “Details” button). By default, this might be set to “Automatic.” Click the dropdown menu and change it to Never (or ensure the toggle is off, preventing auto-join). From now on, if your Mac loses its primary internet connection, it will simply disconnect. You can still manually tether to your iPhone by clicking the Wi-Fi icon in the menu bar and explicitly selecting your phone from the list.