Shelly stuff is very good and very affordable, good find on this one!
Nice work Maurice!
I would love to do something similar, but without changing the original buttons. I actually use the extra heater when brewing full pots sometimes.
Any advice on how I could be doing this without using a push-button?
Sorry for the really late reply to your question.
Some of these power switches can interoperate with different kinds of switches.
The Fibaro that I used for example, supports both momentary switches (push-button) and toggle switches (rocker). In the switch configuration you can change the mode of operation, to make a simple on/off switch work.
I didnāt make use of this, simply to make the switch more predictable. I push on the left side of the switch to turn on the device. With a rocker switch, you have to toggle the switch to flip the power state, and that might be either pushing it left or right.
On thing to beware of, is when the rocker switch has a light built-in. If I remember correctly, the switch position is hard-linked to the light state. Therefore, it wouldnāt be possible to turn on the button light when itās in the OFF position and you would enable the smart switch remotely. An alternative would be to use a rocker switch without a light in it, and install an extra status light that you power from the smart switch. I would go for a round light, since those are most easy to build in by drilling a round hole in the enclosure.
Hope these hints help!
Regards,
Maurice
I modded my old Moccamaster as well. Thanks for the inspiration!
Instead of a Fibaro, used a Sonoff Dual R3 to provide the smarts. The Sonoff has an ESP32, so I flashed it with ESPHome. That opened up clever programming possibilities, more of which later.
I replaced the two on/off switches with the very same momentary switches that youāre using. For indicator lights, I used two round neon ones, also per your suggestion. I drilled holes for the lights left and right of the switches.
Like the Fibaro, the Sonoff Dual R3 measures power. Technivorm says we should use the extra heat switch to pre-heat the glass jug while brewing, and keep it on if more than 5 cups are being brewed. I followed their advice to the letter.
When the Moccamaster is turned on and the Sonoff determines from the power consumption (>100W) that the coffee maker is indeed brewing, it automagically applies extra heat. It also measures the time taken to empty the water tank by monitoring the power consumption. If itās 180 seconds or more, my electronic barista deduces that more than 5 cups were brewed, so the extra heat can stay on. All this can be overridden by pressing the switches. In fact, the extra heat should be turned off manually when 5 cups or less are left in the jug. After all, the Sonoff can measure power consumption, but not coffee consumption.
I also made it so that thereās an auto power-off after 40 minutes. Thatās in accordance with EU directive Nr. 801/2013 (EU critics can come up with a more palatable excuse). Helpfully, HASS sends a notification to my phone to remind me not to waste the coffee still left in the pot. Likewise, thereās a phone reminder when brewing is done.
It was an enjoyable project, but whatās best, itās actually useful! It saves squirrels and pretty trees, too!
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+1 for the liberal use of Wago 221ās! 
Power sensing, auto-off and reminders sound like great added value.
Thanks. Gotta use all them Wagos, because the wiring got more complicated with two momentary switches and two indicator lights in the picture.
I used velcro tape to stick the Wagos and the Sonoff to the aluminium frame. Itās not a good idea to let any of them rest on the bottom plate, because any coffee that drips onto the hotplate can leak inside and cause havoc. Technivorm would do well to fix this ā if they havenāt already.
Nicely done @epollari !
Cool idea to have the high power consumption time determine the number of cups 
I only use it for signalling ācoffee is readyā (which is 30 seconds after the power drops down, by which time the filter dripping is ready).
Auto power-off is something I do too. My home assistant sends me a telegram message to notify me about coffee getting lost when I donāt act quickly. Also a nice trigger for knowing that I have been concentrating too much on coding and too little on drinking coffee.
Thanks. Your pioneering work benefited me greatly.
Even if you donāt use extra heat, you may want to count the cups to predict how long it takes for the coffee to drip into the pot. Obviously, it varies according to the number of cups. The filter basket on mine lacks the automatic drip-stop and patience isnāt my strong point, so Iām forever cleaning the hotplate. There must be a simple formula for predicting the exact drip time. I guess Iāll have to time it with various loads.
Why arenāt you using HA Companion App notifications instead of Telegram?
I implemented the Telegram notification before the companion app was supporting app notifications IIRC. One of these days, I will be re-implementing my whole setup, and then the companion app is definitely going to be my weapon of choice.
There are some nice perks to the HA Companion app. I donāt need to be reminded that an auto-off occurred yesterday, so Iāve set the notification to expire and hence, disappear after a while. Also, Iāve included a shortcut to the coffee makerās virtual on/off switch, so itās extra easy to give myself extra time to finish the pot.