Is your internet moving a little slower than usual? Are you seeing hints of devices you don't recognize in Windows Explorer, or when you cast media to your TV? If you suspect a neighbor is stealing your Wi-Fi, here's how to check (and boot them off).
"So someone's watching Netflix on my internet," you may say. "What's the big deal?" Even if you have a little bandwidth to spare, you probably don't want other people on your network, especially if it's unsecured. If someone has access to your network, they have access to all the computers on that network, and that's dangerous. They could access files you're unknowingly sharing, they could infect you with malware, and in certain situations they could even steal your passwords and other personal information.
As a result, you should take care to make sure each device connected to your network is one you can trust. Thankfully, there are free tools that'll help you see everyone on your Wi-Fi right now.
See Who's On Your Network
Windows users can download a free, portable program called Wireless Network Watcher (scroll down to the Zip download link below "Feedback" to get it), and Mac users can download a free, slightly more complex program called Who Is On My WiFi from the Mac App Store. Both tools will provide a list of every device currently connected to your network, so you can identify the ones that belong to you.
Wireless Network Watcher
To use Wireless Network Watcher, just launch the program, and it will immediately begin scanning your network. This will take a minute or two—you'll know it's working if the bottom-left corner reads "Scanning..." Once it's done, that message will disappear, and you'll be presented with a full list of connected devices.
The resulting list may look a little cryptic, especially if you aren't super tech-savvy, but don't worry. You can ignore the IP address and MAC address listings for now. If you're using Wireless Network Watcher, just focus on the "Device Name" and "Network Adapter Company" columns. For example, I see an item named "Dulce" in Wireless Network Watcher, which is the name of my wife's MacBook. I see another with no name, but with "Philips Lighting BV" as the network adapter manufacturer, which means it's probably the hub for my Philips Hue lights. You can double-click on a device to add "User Text" that helps you identify each device, which will help you narrow down all the items in this list.