Doing a search, it seems it could be anything, it is a chip that is used in a fair few IOT devices.

I think you might be right. The UniFi Network app on my phone tells me it’s a Texas Instruments chip, WiFi 4 @ 2.4 GHz.

Still loads of legacy IOT stuff that runs on good old 2.4G

If I had a mystery device connecting to my network I would power every Wi-Fi device off and see if it is still connected and then add each device back slowly until it reappears.

In reply to a post by dect:

If I had a mystery device connecting to my network I would power every Wi-Fi device off and see if it is still connected and then add each device back slowly until it reappears.

There’s something slightly quirky about these too as the MAC address they’re reporting internally is different to the MAC address they’re advertising with the router and getting sniffed by the UniFi cloud key device / app. I’ll need to have a better look.

In reply to a post by dect:

If I had a mystery device connecting to my network I would power every Wi-Fi device off and see if it is still connected and then add each device back slowly until it reappears.

I'd change my WiFi WPA passphrase. Some security teams advise changing this yearly anyway. Its one reason I'm avoiding WiFi smart home kit (e.g. smart power sockets/bulbs)....

In reply to a post by Pheasant:

I think you might be right. The UniFi Network app on my phone tells me it’s a Texas Instruments chip, WiFi 4 @ 2.4 GHz.

Still loads of legacy IOT stuff that runs on good old 2.4G

Most IOT, even new things, run at 2.4Ghz. Maybe the Wi-fi chips are cheaper, or they do it to make sure it is compatible with all routers. I got some window/door sensors and they are all 2.4Ghz, I really should have got Zigbee ones. A lot of them are made by chinese companies

In reply to a post by dect:

If I had a mystery device connecting to my network I would power every Wi-Fi device off and see if it is still connected and then add each device back slowly until it reappears.

It is strange, in the clients section on the network map they are not there and everything is accounted for. But if I go into the advance part and DCHP server they are there, or they were, seems to have gone now. The only things i can change on the DCHP server page is IP Address Pool, Address Lease Time, DNS servers and the gateway. The list of clients is just that, a list I can refresh.
It is the clients section on the network map that I can change stuff, but as I said they don't appear on that

In reply to a post by jchamier:

I'd change my WiFi WPA passphrase. Some security teams advise changing this yearly anyway. Its one reason I'm avoiding WiFi smart home kit (e.g. smart power sockets/bulbs)....

I don't think they are available, I think the router is just picking them up, just like your phone would pick up a Wi-Fi signal. The chances of anyone guessing my Wifi password is pretty slim and to be honest the majority of people around here their own broadband, while I am not sure about the Indians across the road, I don't think anyone close to me have the skills to crack a WPA2 never mind WPA3.

Changing the password every year would be a nightmare.

In reply to a post by Pheasant:

There’s something slightly quirky about these too as the MAC address they’re reporting internally is different to the MAC address they’re advertising with the router and getting sniffed by the UniFi cloud key device / app. I’ll need to have a better look.

I have heard of that before, I know Mac address can be spoofed, but I don't see any reason why a IOT device would need to spoof the Mac address

In reply to a post by zyborg47:

In reply to a post by Pheasant:

I think you might be right. The UniFi Network app on my phone tells me it’s a Texas Instruments chip, WiFi 4 @ 2.4 GHz.

Still loads of legacy IOT stuff that runs on good old 2.4G

Most IOT, even new things, run at 2.4Ghz. Maybe the Wi-fi chips are cheaper, or they do it to make sure it is compatible with all routers. I got some window/door sensors and they are all 2.4Ghz, I really should have got Zigbee ones. A lot of them are made by chinese companies

As you say. 2.4 also has better range/penetration than 5 and the data throughput requirement on many IOT devices is pretty humble. So 2.4 fits the bill.

In reply to a post by zyborg47:

In reply to a post by Pheasant:

There’s something slightly quirky about these too as the MAC address they’re reporting internally is different to the MAC address they’re advertising with the router and getting sniffed by the UniFi cloud key device / app. I’ll need to have a better look.

I have heard of that before, I know Mac address can be spoofed, but I don't see any reason why a IOT device would need to spoof the Mac address

It’s not spoofing per se and these devices aren’t clever enough (or have the need) for any MAC randomisation algorithms ala Apple. It’s not very high on my list of priorities as it works as intended.