PublicIPChecker

Guide

How to tell if someone is using your Wi-Fi

5 min read · Updated 2026-10-06

Spot unknown devices on your network using your router's client list, remove them, and lock your Wi-Fi down with WPA3, a strong password and WPS disabled.

On this page

  1. Signs to look for
  2. Check your router's device list
  3. Other ways to spot intruders
  4. Remove them and lock the door
  5. What this looks like from outside

A neighbour borrowing your bandwidth is annoying; a stranger on your network is a security problem, because they can reach local devices — printers, cameras, a NAS — that your router would otherwise never expose to the internet. The good news: your router keeps a list, and removing someone takes two minutes.

Signs worth investigating

  • Slower speeds than usual, especially in the evening, on a connection that was fine before.
  • Extra activity on the router's lights when nothing of yours is using the network.
  • Unexplained devices in the router app or admin list — a phone, laptop, console or IoT plug you do not recognise.
  • Configuration changes you did not make — a new Wi-Fi name, DNS server or port-forward rule. This is the serious one; change your admin password immediately (see finding and securing the router page).
  • DHCP lease exhaustion or an IP conflict appearing out of nowhere.

Fatigue, ISP congestion and a failing router all produce slow internet too, so confirm with the device list before blaming a neighbour.

Check your router's device list

  1. Open the admin page at the gateway address — the router IP guide shows how to find it on any device. Most ISP apps (Xfinity, BT, Sky, Eero, Google Home, TP-Link, Asus) show the same list more conveniently.
  2. Find Connected devices, Clients, DHCP leases or Attached devices.
  3. Compare with your own hardware. Manufacturers appear in the MAC prefix — see MAC vs IP — which usually makes identification obvious: three Apple devices, two TVs, a printer, eight smart plugs.
  4. Note the timestamps: a device that has been connected for weeks is likely a forgotten gadget; one that appears only at night is worth a closer look.

Other ways to spot intruders

  • A scanning app (Fing, Advanced IP Scanner, nmap on a laptop) lists every host that answers on your subnet, including ones the router under-reports.
  • ARP table check: arp -a on a desktop shows what your machine has recently talked to on the local network.
  • Guest network audit: if you have a guest SSID, check its client list separately — intruders often land there because the password is simpler.

Remove them and lock the door

  1. Change the Wi-Fi password (and the admin password) — this evicts everyone, including the intruder. Do it from a wired or already-connected device.
  2. Use WPA2-AES or WPA3, never WEP, TKIP or open.
  3. Turn off WPS, the push-button pairing feature with a documented history of brute-force attacks.
  4. Turn off remote administration on the router and disable UPnP if you do not rely on it — see port forwarding.
  5. Keep firmware updated and, if you must block a specific device, use a MAC filter as a speed bump, not as security.
  6. Re-check in a week. If unknown devices return, a device on your network — or a compromised camera or plug — may be the culprit.

What this looks like from outside

Here is the part people get wrong: every device in your home shares one public IP address, so a visitor on your Wi-Fi appears to the internet as you — see public vs private IP. That has two consequences:

  • You cannot spot an intruder by checking your public IP. The IP checker shows one address for the whole household; counting devices requires the router's list, which is a local view.
  • Their activity affects your address's reputation. If a guest downloads malware or scrapes a site, the block lands on your address — that is IP reputation, and it is why an ISP abuse letter may arrive for something you did not do.

A separate guest network is the clean answer: guests get internet access and cannot reach your printer, NAS or admin panel — and if something goes wrong, you reset one password and rotate the SSID.

Bottom line: check the client list, change the password, disable WPS, and put visitors on a guest SSID. Your public IP is shared by design, so the router's device list is the only place the intruder is visible.

Frequently asked questions

How can I tell how many devices are on my Wi-Fi?

Your router's admin page or app lists every client with its MAC address and hostname. Scanners such as Fing or nmap give a second opinion. There is no way to count devices from your public IP address — the whole household shares it.

Can my ISP see how many devices are on my Wi-Fi?

Not directly. The ISP sees your connection and its traffic patterns, but NAT hides individual devices; a carrier-grade NAT provider sees even less.

Will my IP change if someone steals my Wi-Fi?

No. Everyone on your LAN shares the same public address, so their traffic looks like yours. Changing the Wi-Fi password removes them; changing the public IP requires a new DHCP lease or a VPN.

Keep reading

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Investigating a suspicious login, a spam email header or a server log entry? Run any IPv4 or IPv6 address through the same geolocation and proxy checks.

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