Monthly Archives: September 2020

Automations in HomeKit

Last night I was refining some of my HomeKit automations (rules) and it occurred to me that it might be an idea to capture some tips from the last few years.

HomeKit versus HEMS functions

I currently have around 30 automations delivering:

  • Space heating – 8 eTRVs / smart valves linked to a smart plug for boiler control and both movement and window sensors.
  • Window management – 4 window sensors and a movement sensor indicating via colours smart bulb when windows are left open (typically checked prior to leaving the house)
  • Lighting control – dusk-to-dawn lighting with colour-override by window management.
  • Watchdog – robustness aid.
  • Wet goods – control and dishwasher and washing machine in conjunction with HEMS.

In total I currently have:

  • 8 smart radiator valves (eTRVs)
  • 6 smart plugs
  • 4 door / window sensors
  • 3 smart bulbs (two coloured + 1 on/off)
  • 2 movement sensors
  • 1 environment sensor (temperature, humidity, air quality)

So, what are my tips:

It Is much more intuitive to write rules in the Eve app.

  • The free Eve app can pretty much do everything that Apple’s own Home app can do for HomeKit devices (not just Eve’s own devices). The construction of rules in the form: IF {any of one of more triggers} AND {all of none or more conditions} THEN {set one of more scenes} is very intuitive in the Eve app.
  • Eve also allows rules to be names, whereas Apple’s own Home app sets names to a trigger condition, so if you have many rules as I do with common triggers then you end up with a confusing list of rules with duplicates names which need to be opened to tell one from another.
A rule in the Eve app.

Comparison with conventional logic. Simple IF rules are very straightforward: IF {any of one or more triggers} THEN {set one or more rules}, however AND rules take a bit more thought: IF {list of AND conditions} AND {same list of AND conditions} THEN {set one or more scenes}.

A watchdog makes execution more robust. HomeKit rules are triggered by changes of state such as going from open to closed or from movement to no movement, but if some some reason a trigger is missed you may have the wrong scene set for hours. My watchdog rechecks rules every 5 minutes as described here.

AND rules. AND rules may be converted to use the watchdog principle by simply adding an additional trigger to reference the change of state of the smart plug used for the watchdog: IF {original list of AND conditions + new smart plug trigger} AND {original list of AND conditions} THEN {set one or more scenes}.

Simple IF rules. IF rules with single triggers are easily converted. The same principle applies to AND rules: If {original single trigger + new smart plug trigger} AND {original single trigger} THEN {set one or more scenes}.

Complex IF rules. IF rules with multiple triggers are more involved to convert to the watchdog principle. If you just add the smart plug to the trigger list as per the earlier AND paragraph then the rule triggers every time the smart plug cycles. If you were to add the other triggers to the conditions list then the rule would become an AND not an OR. Instead to convert an IF with multiple triggers then it needs to be converted to multiple rules – one for each original trigger condition – all driving the same scene. Each of the new rules is an IF with a single trigger as per the earlier paragraph. The existence of multiple rules setting the same scene(s) creates a multiple-trigger IF.

Multiple hubs. Having multiple hubs (in my case two Apple TV’s) can make the system more robust both during occasional software updates (it’s improbable that both will update simultaneously) but also by extending Bluetooth robustness (hubs commonly communicate to devices by Bluetooth but between each other by WiFi). Obviously the hubs need to be placed in different parts of the home. (Eve Extend can also be used to reach out-of-range Bluetooth devices over wifi, but isn’t compatible with my older 2015 Eve Thermo eTRVs.)

Contrasts in Smart Lighting

We recently enjoyed a week’s holiday at Pevensey Bay. The home that we rented, like our own, includes many smart features but there are some similarities and differences in approach. One area of difference in smart lighting.

The Studio, Pevensey Bay

Both our own home and The Studio have smart lighting but differ in approach. Our own smart lighting concentrates on smart bulbs, while The Studio (with the exception of the kitchen) concentrates on smart switches. So why choose one approach over the other?

At our home we have a handful of smart bulbs, with standard dumb switches. The bulbs incorporate functions like dusk-to-dawn lighting and colour change for status indication (open windows, movement in garage etc). At The Studio there are a large number of smart switches controlling an even larger number of standard dumb bulbs.

So let’s think about choices:


If you are going to control multiple bulbs together on one circuit then it’s generally cheaper to have one smart switch than multiple smart bulbs.

4 gang Lightwave switch

Coloured smart bulb


Smart switches can either control on/off or act as dimmers, but they don’t vary colour. Some smart bulbs can vary colour. If you want to control colour then you’re going to need some sort of remote control (like The Studio in the kitchen) or access via smart device like a phone or tablet.


Most smart light switches require a neutral wire. However many UK homes do NOT provide a neutral wire at the switch. A typical UK light switch has a live, switched live and earth only (I.e. no neutral) although there may be confusion as the switched live is commonly blue (or black in older homes) like a neutral would be.

Adding a neutral can be relatively costly as it requires a new cable between the ceiling rose and the switch. If having a re-wire it’s worth adding neutrals to the specification just in case.

Typical ceiling rose wiring UK.
Example automation


Both switches or bulbs can be automated via a smart hub for on/off or brightness to respond to time-of-day, movement, door or window opening etc; so that’s not really grounds to chose between smart switches or smart bulbs.

What about combining smart switches and bulbs on the same circuit?

In short I don’t really know why you’d want to. Even if it worked properly you’d have incurred extra cost for the second smart device for limited benefit as you’ve duplicated the smart functions, but it’s likely not to work properly. Even with simple on/off functions the smart bulb will be missed by the hub when the power is off at the switch (although some ecosystems allow this error to be masked), but with dimmers it will probably be worse as the bulb may not function correctly when the dimmer is set to less than 100% brightness.

You might consider using the smart switch as an smart button without using the switched output, and feed the smart bulb from a permanent live, but that’s not combining them on the same circuit. This could be achieved physically by something as simple as moving the switched live output to the live input on a switch. However the two smart devices, switch and bulb, would then need to be linked entirely programmatically through the hub. That would be at least two automations in HomeKIt – an ‘on’ automation and an ‘off’ automation.


There isn’t a right answer whether smart switches or smart bulbs are best. The best choice will depend on your situation.

Inducted into the hall of fame

One of the features of our home is the all-electric kitchen. We do have gas for space heating and as a back-up on the hot water for days that are both dull and have relatively high cost electricity, but the kitchen is all-electric. I have to say that this was not our choice, rather the kitchen came that way when we bought the house five years ago. We have replaced the oven in the meantime, but until today the hob was that bought with the house.

Unfortunately the hob suffered a failure of the two of the rings and today we’ve replaced it like-for-like with a new inductive unit. Inductive is attractive as it’s relatively efficient, but I was struck by the fact that the one hob required a 32 Amp supply, but the new one manages with a 13 Amp plug.

Bosch PUE611BF1B inductive hob.

So, by what magic does the new hob use less than half the power of its predecessor?

itemold hobNew hob
Smallest ring1,200 Watts1,400 Watts
Second smallest 1,400 Watts1,800 Watts
Second largest1,800 Watts1,800 Watts
Largest ring2,200 Watts2,200 Watts
Total *6,600 Watts3,000 Watts
Tabulated of maximum non-Boost power per ring with manufacturer’s total

The first thing to observe is that the sum of the ring powers does not equal the manufacturer’s total for the new hob, although it does for the old hob. The second would be that the sum of the new ring powers at 7,200 Watts is more than the sum of the old ring powers even though the required total is less!

The answer is that the new hob features power management capability. In any hob the rings will spend much of their time cycling on and off to maintain the required heat. In the old hob all the rings might on at one time drawing maximum power, but a few moments later they might all be off. However the power management in the new hob the total power would be levelled out so that the average over time might be the same, but the peaks smaller and the troughs shallower.

For most people this levelling out of the power demand would pass unnoticed, but for us it could be quite useful.

We do most of our cooking in the evenings for which, particularly in winter, power is taken from our Powervault storage battery with any excess from the grid as illustrated by the series of evening spikes in the image to the right. The Powervault has a relatively limited maximum power (hence the spikes) but as the new hob has power management then any spiking beyond battery maximum power capability should be reduced thus avoiding what, for us, could be peak rate electricity at 35 p/kWh on our dynamic smart tariff which is a direct cost save.