AirPort Extreme usage

We will assume.......(never a smart thing to do)........that you have a Mac computer

Open AirPort Utility (Finder > Applications > Utilities > AirPort Utility)

Click directly on the picture of your AirPort router and a smaller window will appear with information about the AirPort

Look for the listing of "Wireless Clients" to see a list of the devices that are currently connected to your WiFi network. For example........

Using the Timed Access feature of AirPort Utility, you can set up separate "rules" for each device that will specify the times that the device is allowed to connect to the WiFi network.

For example.......you could specify that Junior's iPhone can only connect to the WiFi network between the hours of 8:00 AM and 11:00 PM each day. The iPhone would not be able to connect to the WiFi network at any other times.

At the same time, you could specify that another device like your Mac will have unlimited access, meaning that it can connect at any time.

To locate Tmed Access. in the AirPort Utility application.......

Open AirPort Utility

Click on the picture of the AirPort

Click Edit in the corner of the smaller window that appears

Click the Network Tab at the top of the next window

Enter a check mark next to Enable Tmed Access if the box is not already checked

Click on Timed Access Control

For more information, click on the Help menu at the uppermost top of your computer screen

Click on AirPort Utility Help

Click on Table of Contents

Click on Control Access to your WiFi Network

You could set up a rule in Timed Access for the "unknown client" to have "No Access", so they could never connect.

But before you do this, you might want to make sure that the unknown client is not your printer, security camera, doorbell, thermostat, television, garage door opener,etc that you may have forgotten about.