The Unwanted Data Drain
If you own an iPhone and a Mac that are signed into the same Apple ID, macOS features a highly integrated “Personal Hotspot” system. When your Mac loses its standard Wi-Fi connection, it will often automatically detect your iPhone nearby and seamlessly connect to its cellular network to maintain internet access. While this feels like magic, it can be a financial disaster if you are on a limited or pay-per-gigabyte cellular data plan. Your Mac might automatically download a massive 5GB system update or sync a giant Dropbox folder over your iPhone’s connection before you even realize what has happened.
Breaking the Automatic Tether
To protect your cellular data allowance and stop macOS from aggressively tethering to your iPhone whenever the primary Wi-Fi drops, you must disable the automatic hotspot connection feature.
Click the Apple logo in the top-left corner of your screen and select System Settings. In the left-hand sidebar, click on Wi-Fi. Scroll down to the very bottom of the main Wi-Fi panel until you find the section labelled “Personal Hotspot.” Here, you will see a toggle setting named Ask to join Personal Hotspots. By default, this is often set to “Automatic.” Click the dropdown menu and change this setting to either Ask to join or Never. If you select “Never,” your Mac will treat your iPhone like any other standard Wi-Fi network; you will have to manually click the Wi-Fi icon in the menu bar and explicitly select your iPhone from the list to establish a tethered connection.