Someone else is using my Wifi System for their Sonos

Are you using the same SSID (name) and password as the old house?

Which SONOS controller are you using? Mac? PC? iOS? Android?

Are you sure that you are using your own WiFi, not the neighbors? If you were using a neighbor's WiFi while waiting for your own installation, you should now "forget" their WiFi.

Avoid the temptation to factory reset anything because this will complicate your issue.

Here's a short test. Grab you phone and set it to Wi-Fi discovery mode. Now go turn off your router. Back to your phone and set it to rescan for Wi-Fi networks. Has your network disappeared? It should have.

The purpose of this is to see if there's a Wi-Fi network with a similar name to yours still present.

Switch your router back on and let it reboot. Once finished, go in to the settings and change the IP address. So if it's 192.168.0.1 change it to 192.168.1.1 When you hit Confirm or Apply you'll lose your connection to the router. That's okay and to be expected. Just type in the new IP address in to your browser search bar.

Next, after logging in again, change the router's admin password. The defaults might be:

Admin login: admin
Admin password: user

That's how your friend is able to access your route, if indeed that's what's happening.

Once you change the password then the casual hijacker is locked out. Remember though to write down your new password somewhere you can always get to it.

Now login again with the new credentials. Now set up a new wireless SSID and a new password for that. Now go set up your Sonos system and make sure your phone logs on to the new settings.

Determined hackers can use packet sniffers to still break in to your Wi-Fi. That's a more difficult problem to solve, but let's see how you get on with this after making the changes above. 🙂

I cannot help suspecting some user confusion here, as this sounds so odd (sorry).
One possible explanation here is that the neighbour's wifi is unsecured and the OP's controller is connecting to that wifi while thinking they are connected to their own.

So to the OP. Please check again that your phone is connected to your wifi network, not another one.

Edit: actually I am really just agreeing with @buzz here, now I look back. But it seems so unlikely that having changed your own wifi password anyone else could get access it. This doesn't feel like a determined hacker situation.

Now I quite want to know what the problems turns out to be. Please let us know.

(I am confident that the above posts will solve the issue.)

A friend down my street said he'd found someone accessing his router/ wifi. Considering his SSID and passkeys were very obscure he couldn't work out how they'd managed to log in.

Hacking is possible, but not normally with the aim of setting up your Sonos system on somebody else's network.

Keithmac wrote:

A friend down my street said he'd found someone accessing his router/ wifi. Considering his SSID and passkeys were very obscure he couldn't work out how they'd managed to log in.

If one digs around, there are WiFi hacking kits. Your friend can make things more difficult for the hacker if he changes the router's admin password and doesn't allow router configuration editing over a wireless connection. In any case, frequent changing of the WiFi passwords is recommended. This will not absolutely shut out the hacker, but password changes will increase his workload and hopefully encourage him to pester easier targets.

A helpful strategy would be to switch use to the 5GHz band and turn OFF the 2.4GHz band or setup the 2.4GHz band for "Guest" access only. Guest access will limit the hacker to outward Internet access on 2.4GHz and keep him off the local network. 5GHz does not travel as far and hopefully this will keep the hacker out of range. Of course this might create some range issues for the regular users too. If the hacker's intent seems to be for poaching your friends Internet connection and your friend has an advanced router, using the 2.4GHz Guest strategy could be enhanced by throttling the speed of this connection -- thus making it very unattractive.

Take care when pursuing this sort of "arms race". If you are too aggressive, you'll challenge the hacker's intellect and he'll accept the challenge. Rather, appear to be totally inept. Hopefully, he'll get bored and move on.

If you're really sure that the offender IS using your router and WiFi to run their SONOS setup, AND if as you say you are able to see and control his SONOS system, this sets up some amusing possibilities for retribution. I would think that a few doses of The Stars and Stripes Forever at high volume at 3 AM might make them rethink the setup.