I think this is a fairly common issue for smart home accessories. It’s probably a problem with them using a cheap Wi-Fi chip. @glennf do you know any more about this particular limitation?
For people with Eero routers who encounter this issue (I have occasionally), open the Eero app, tap “Settings”, tap “Troubleshooting”, tap “My Device Won’t Connect”, then “My Device is 2.4 GHz only”. This will disable the 5G radios for ten minutes while you set up the new equipment.
Once the device makes its initial connection, it should be fine from that point on.
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Yes, I had this problem with my smart thermostat, a Sensi, which, after a neighborhood power outage, would not reconnect to my network. I have five base stations of various kinds. After a lot of HomeKit and front-panel frustration, I realized that the Sensi only connects over 2.4 GHz—this is apparently true of a lot of HomeKit devices.
So I set up a guest network on my main router, which was exactly beneath the thermostat:
- Unique 2.4 GHz network name
- Enabled access for guest network to reach rest of main network
- Connected Sensi to that network
Immediately solved the problem. This also helped me diagnose a problem with two HomeKit cameras this week as well. I have an upcoming Mac 911 article about this whole issue!
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@glennf , I’ve heard the justification that 2.4 GHz bands are used for many of these devices because while that band is limited in frequencies it tends to have a longer range than the 5 GHz bands. Therefore it’s more suitable for a device like, say, a door lock that may be farther away from the router.
Is there any truth to that?
Yes, the 2.4 GHz band has a longer wavelength than the 5 GHz (or newer 6 GHz) band. The longer wavelength makes it less susceptible to having signals absorbed by typical wall and floor/ceiling materials, although bricks are an issue as they can retain moisture. 2.4 GHz signals can be readily absorbed by water, which is why microwave often oscillate in the 2.4 GHz band. We are also water bags, and Boeing at least tested its Wi-Fi in planes by using sacks of potatoes as human analogues for absorbency! (See my best Economist article headline, “Coach Potatoes.”)
However, the other reason is surely cost. A designer can put in a several-year-old, super-cheap radio design that’s single band and has no fancy MIMO or other features—or those features are 100% built into silicon, requiring no additional chips—and shave cents to dollars off low-cost products. The rule I recall is that the bill of goods should be < 10% of the retail price, but 5% is better. So a $2 bill of goods is a $40 retail product (sold via wholesale at $20 to $30).
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As Glenn says, the 2.4GHz signal is supposed to be better at penetrating internal walls.
In any case, with my latest wifi 6 router, the Wifi Explorer app (for Mac) reports my 5GHz band is a better signal in most areas of the house. But it also reported that the 2.4GHz band is very crowded (with neighbours wifis) so the router probably has a hard time deciding on the optimum channel for the 2.4GHZ band.
I also have band-switching enabled on the router (by default). This means the router can suggest to a compatible device that it use 2.4 or 5GHz at any time.
Sounds like Glenn’s forthcoming article will cover this and other Homekit/wifi issues.
At least I now have everything working for Christmas. 
Cheers everyone
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For sure. Remembering my first Airport router, and the full size compact flash card inside with the WiFi transceiver. Mini means money in chip terms.
Thanks for the explanation!
Switching to 2.4 GHz definitely helps with connection issues for smart devices, especially if you’ve got a lot of them! It’s slower, but it has a better range.
Shorter wavelengths have more penetrative energy to penetrate walls etc. This is classic physics and we use it in Medicine as well. But some exceptions apply (see below) for non-GHz information in Medicine (not the same as 2.4 vs 5 GHz.
Happy Holidays
UVA 320-400nm Penetrates window glass and enters skin
UVB 280-320nm Does not penetrate window glass
UVC <280nm STRONG
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