O
I'm struggling to see how enabling 2 way comms and playing with MACs is cheaper than a divider in the chip.

Measuring low frequecies accuratly is more difficult than you think.
What you have to do is count cycles in one second yuod get perhaps 47 or 53 so you need to average it out especailly in times of high or low demand.
So you need to sample it for at least 10 seconds to giove you 0.1 resoultion and in that time the situation can change.

Its not hard at all, just time the number of clock cycles between 2 successive crossings. You could average lots of counts but I don't believe there's a need to, a small percentage of mistimes is immaterial in practice. Simply averaging several yes or nos would be trivially easy.

Anyway it would be cheaper to have just one device measuring frequency rather than every electrical device each reading it. If I were designing such a thing it'd use teh smart meter to measure it rather than install the ciruitry in my kettle and fridge.freeze, TV cooker shower , washing machine, coffee maker storage heaters fires hair dryer etc.....

but you'd still need to install everything in the appliances, you'd only miss out the clock divider, which inside a custom single IC costs close to nothing.

What I'd get manufactiers of such devices to do it allocate a specific number to each product a bit like a MAC address which my smart meter can locate and be able to either just switch off/on or reduce it's power.

more costs

idf all 2KW+ kettles had a 1/2 power switch then my first try would be to turn those kettles is 1/2 power them, I wouldn't turn off motors or mmoving things such as food blenders.

I'd agree there. There are many things can be turned off or down if its ever worth it. Today its mostly not though.

and send the appliance serial number down the wiring now and then, and the power co software will automatically knock £1 off the bill.
Too much hassle and no need for it.
The user needs some reason to spend the cost of the control unit. If I were offered 20% ROI I'd buy, for a prize draw I wouldnt.
You don;t need to you make it cheap enough that no one would bother

that'll happen, but only after its already being widely bought, ie produced on a mass scale, with all the upfront investments paid off. To get to that point its going to cost, so there must be a customer upside.

or you make it illegal to sell products without such things.

but then its a protected parasite, & the cost stays high.

We do this in the name of H&S, you can't normally buy appliences without leads, you have to buy them with the product or buy them seperatly.
I remmber the days when buying electrical equipment you HAD to purchse a lead or plug and put that on yuorself. Nowadays that's not possible for most people you can;t go and buy even a £5 kettle without a moulted lead.
You can't say IO'm not buying an electrical product that comes woth a free lead because i have plenty. I have about 150 IEC leads I'm not using in a box.

Firstly this isnt a H&S issue, and there isnt anywhere near justification to force it on everyone. Second, phones are beginning to be sold now without chargers, and with IEC leads so common theyre moderately likely to become optional with cheap appliances. Government interference gets in the way of progress more than it helps it.

NT

Better to work the system on voltage fluctuations than frequency.
If the voltage drops, reduce the load by what ever means you decide
on. When it rises the cut off loads can be reconnected.
Much easier.