If you notice a device that shouldn’t be on your network, you can restrict it from accessing the internet by blocking it from the connected device list.
If you’re using the iOS version of the app, tap on the Devices tab to open the list of connected devices. You should see devices separated by category, with recently connected devices appearing below this.
You can tap on any device on this list, then scroll to the bottom of the menu that appears and select Block From Network to disable network access on that device.
Blocked devices will now appear in a new list that populates at the bottom of the home screen. You can tap on any device on this list to remove it from the block list, which will re-enable network access.
Note: Device blocking is not available in bridge mode.