How to Know If Someone Is Using Your WiFi: Get an Alert for Every New Device

Most people find out about a strange device on their network by accident, weeks later, if at all. It's much better to be told the moment it joins. In this video we'll set that up, and make sure you're not woken by a phone that just came out of standby.

As always, this is DeviceShelf's demo network, a made-up home with forty-four devices.

Alerts need a watcher. Click the Auto button next to the filter. With background monitoring on, DeviceShelf scans the network by itself, every five minutes by default. You can choose a shorter or longer interval here, and see when the last scan ran and when the next one is due.

Watching only works while the app runs. Under Settings, General, you can turn DeviceShelf into a menu bar app that keeps going when you close the window, and start it automatically when you log in. Then it keeps an eye on the network in the background without being in your way.

DeviceShelf remembers every device it has ever seen, by its hardware address. When one turns up that has never been there before, it counts as new. The button with the sparkle shows how many are waiting for your answer. Here there are two.

Open one, and DeviceShelf asks: new device, is this yours? A new phone in the family, a visitor's laptop or the new smart TV: answer once, and the device stops counting as new.

Click Yes, it's mine, and that's it. If you don't recognize a device, click Ignore and lock it out in your router's settings. DeviceShelf points you there with the Open router button.

One thing that surprises people: phones use a private Wi-Fi address, a made-up hardware address per network, and some rotate it now and then. DeviceShelf marks such devices and recognizes them by their name instead. Only a phone without a stable name comes back as new after it rejoins. Give it a name in its details, and it stays the same device.

Now to the alerts themselves. Under Settings, Alerts, the first switch turns on desktop notifications: a new device, a device that went offline, a device that came back.

Every alert also lands in the bell at the top of the window, so nothing is lost if you miss the notification. The bell keeps the list even with notifications switched off.

If you'd rather get an e-mail, enter your own mailbox here. For Gmail, Outlook, iCloud and the other big providers, DeviceShelf finds the server by itself. You only need an app password, which those providers create for exactly this purpose. Several alerts within a few minutes are bundled into one e-mail.

For everything else there's the webhook. DeviceShelf sends each alert to an address of your choice, for example an IFTTT applet or a Home Assistant automation that switches on a light when a stranger joins.

Quiet hours keep it silent at night, and maintenance windows cover planned work, like the evening you rebuild your network. The timeline still records everything in between.

The biggest source of false alarms is phones. They switch off their Wi-Fi while asleep and come back an hour later. That's why the standard setting waits for three missed scans before a device counts as offline, and why phones and tablets going offline only go to the timeline unless you switch that on below.

For a single device that comes and goes all the time, like a battery doorbell, open it and mute its online and offline alerts. You'll still be told about anything new.

One last setting: the external watchdog. DeviceShelf pings a service like Healthchecks.io every minute. If the pings stop, because of a power cut or a crash, that service raises the alarm. So silence really means nothing happened, not that the watcher is down.

And the timeline keeps the history: which device joined when, with its address and hardware address. If an alert came while you were away, this is where you look it up.

If you'd rather read a summary than a list, the AI Cockpit has a Digest button: six sentences on the state of the network and what changed since the last look. Here it names the two new devices, the PlayStation and the Pixel phone, and the port that opened on the Docker host. Like every AI feature in DeviceShelf, it's optional and works with a local model too.

So: switch on background monitoring and let DeviceShelf run in the menu bar. Answer the question for every new device once. Pick how alerts reach you: notification, e-mail or webhook. And use the offline rules and mute switches, so the alerts you get are the ones that matter.

More videos on finding devices, bandwidth and security are on our channel. DeviceShelf runs on Mac, Windows and Linux, at deviceshelf dot app.