Like almost everything to do with Android, you can find out who has been sneaking some of your WiFi with an application. There is a free network tool which you can download right from the the Google Play Store called Fing.
The first thing you have to do is connect to your smartphone or tablet to the WiFi network you want you want to test. Now simply download the application, which you can do by pressing the install button below.
Once the installation process is complete, the tool can easily get started finding the trespasser. At the top of the app’s main page, you will see the name of your network as well as a refresh and the settings menu buttons.
Tap on the refresh button update and the application will show what devices are connected to your WiFi network, specifying whether the router is a smartphone or a computer.
There are many other options in Fing, like sending reports, checking open TCP ports and the list goes on. Perhaps one of its best advantages is that users can change the viewed IP name, which allows the user to know who they are on the app and who the infiltrators are. Once you know who the trespassers are, simply click on the intruder and above you will see an option to ‘enter a name ‘. Enter a new name for that IP address, like WiFi thief for example.
How to block unknown trespassing devices
In the event that you’ve located a intruding device, you are able to access the NAT and MAC information and connect to the router in order to block the unwanted guests from accessing WiFi in the future.
On your computer that connected to your router, enter your IP address into the browser. It will ask you for the password and username on your router and if you haven’t changed it, it will be specified in the device.
Now you’ll need to authenticate. The home page of your router will appear, showing a menu. Go to the security tab and enter a new password. (Remember, to connect to WiFi on your phone or your computer, you must enter this new password).
If this isn’t enough, you can block access for other devices entirely. On the Fing application, you will see information from your connected devices. Write down your MAC address (or your MAC addresses, depending on how many devices you have connected) on a piece of paper.
Search for the block devices option on the configuration page which you can open on your computer. In Access Control area, you can filter the MAC (one or more) that you’ve noted down. This will block any other invading addresses that try to infiltrate. Remember that if you choose this option no one else will be able to connect to your WiFi without having turned off the Access control option, which is good to keep in mind for friends or family who are visiting.