Nest is a thermostat with Apple DNA developed by Tony Fadell. Potentially cut 20% to 30% of your US$1000 annual energy bill. Priced at $249, and get your money back in savings in one year. Looks good, too.
The problem arises when the Nest needs to charge itself and neither the heat nor air conditioning has turned on in a while, like on a mild day. Without a C circuit to take power from, it can only charge itself from running the system.
So it pulses the R-W heat circuit in short bursts to get power.
This isnâ€™t likely something that will directly cause a problem, but it is putting unneeded wear and strain on your heating system â€” no way I would allow this.
If you have a boiler that reacts instantly, like the one Arment has, these short bursts can also be annoying. I would suggest Nest take a look at solar-powered Casio watches for Nest version two.
Update 2: Nest teardown. I think the LCD is a square; the cover glass makes it look circular.