I sometimes create a temporary WiFi hotspot on my Android phone so that I can use the 4G LTE network on my other devices like the notebook computer and the desktop PC etc. Recently I realized that I was not getting very good download speeds on the 4G data connection. At first I thought it could be problem with the weak network signal, but later on I realized that some other people were connecting to my ad-hoc WiFi network and using up all of my data. This could happen to anyone and if you do not want to let others siphon up all of your expensive 4G data pack, then you should find out who else is using your WiFi network using a free program for Windows and Mac called Who Is On My Wifi.
The program works for all kinds of WiFi networks and is basically a network IP address scanner. It scans through all the valid IP addresses permitted by a WiFi router (only IP version 4 is supported) and tells you if any device is connected on those IP addresses. If it finds an unknown device on a new IP address, then it notifies you of the fact using a toast notification in the system tray.
If after installation, you see that it displays “no network configured to scan” message on the top of the window, then you will have to modify settings and set a network for scanning. You have to open settings by pulling File → Settings from the menubar. In the settings window, switch to the Scan options tab and place a checkmark against a network that you wish to scan. Then save the settings by clicking on the Save button and you are good to go.
Now back in the main window, you can click on the Scan Now button and it will scan the configured network for all the connected devices. At the end of full scan, which usually takes a longer time if a lot of devices are connected to the WiFi network, it will display the IP addresses, MAC address, connection status and more. If you trust a device, then you can set the Known status for that device. In the paid version of the program, you also have the ability to disconnect a device from this same interface.
Conclusion: If you do not want unknown and unauthorized devices to connect to your WiFi network, then you can use the “Who Is On My Wifi” program to find and block any of the devices trying to connect to the WiFi network. It works on both the Windows and Mac computers.
You can download :Who Is On My Wifi” from http://whoisonmywifi.com/windows/.