In-wall physical dimmer switch I am having trouble finding that has these properties -
Can you advise where you are in the world? EU/UK/US all use different formats. The module @BebeMischa won’t be affected if there is space.
@Fireblade @BebeMischa also, that is not a physical dimmer switch - people want to be able to dim the light the old fashioned way (by using their hands on the switch) - also the physical switch settings must always match what is shown in whatever app is used to control same, and visa-versa…
So, exactly, what this is made for. Placing it behind the existing switch and stay using that old switch 
Replacing the switch.
All homes built in the US after 1985 are required to have a neutral to every light and outlet box.
Post a picture of the plate. I suspect that you may have to make your own switch with a rotary knob.
House built in the 1930’s. The rotating nob or toggler would be on the left side (the right will be controlling something else).
@stevemann I am handy and more than happy to make my own, if possible…
The shelly product mention before is what you want. You pull the switch out of the wall, wire in the device and put it in the back of the box and then put your existing switches back in and wall plate back on. Everything looks the same but now it’s smart.
Actually depending on how wiring is done at the switches in your house, if there is no neaturl wire at the switch then you place the device in box at the light side.
@bkprath we are talking about the switch on the left side only to be replaced with a smart dimmer switch. I have alot of shelly’s all around the house and I love them. The issue here is that we are replacing the dimmer switch on the left with a smart dimmer. I would rather not replace it with a dumb switch and then be able to only dim it remotely through the shelly. People need to be able to dim it from the dimmer switch itself as well - I need both…
Shelly also has this device that might give you what you want. I use a lot of kasa products and they have this switch you could possible use. In both cases you’d need a different wall plate. Here’s a thread on the Kasa hs220.
A Shelly Dimmer 2 will do that for you though. To complete your setup you just need a toggle style double throw, center off, momentary contact switch like the Leviton 1257. The Shelly can then be configured to enable the actions you need.
For example:
Not sure if my ‘trick’ using a piece of foam is feasible on your type of switch, but in my case it worked… so i changed my DPDT switch i to a SPDT switch just by placing a piece of foam under the switch cover
it was for sure a lot cheaper then replacing the whole switch 
Maybe it is possible to do something similar with a piece of elastick or a spring?
@FelixKa , use case question - when the person holds the toggle in the up position, if not already fully bright, the light would continuously get brighter until they let go, and visa-versa with holding it down?
Yes. Pretty intuitive.
@FelixKa I have a Shelly Dimmer 2 and a Leviton 1257 being delivered shortly :-), which will both now go on the left side of that picture. Do you know where i can get a wiring diagram/picture for this specific configuration?
This scenario should be the top right of the 4 diagrams found on the Shelly Dimmer 2 documentation titled “No neutral wiring”.
For the SPDT switch it’s pretty much exactly as shown in the diagram: You’d run one L from one of the L terminals on the Shelly to the L1 on the Leviton and then A1 from the Leviton back to the Shelly on SW1 and B1 to SW2 (or the other way around, depending which way around you install the Leviton).
If in doubt always ask an electrician.
Perfect @FelixKa I should have done all my dimmers this way, I’ve got a couple others in the house that are the ugly “modern” kind (wife prefers the look of the old switches). If this goes well I will then go back and replace those too… I’ll let you know when it’s all done and how it goes, some of the spare stranded cables that I ended up using between the shelly and the switches are overkill - wrong gauge, actually too thick - so I started having to remove some of the strands at the end for the shelly so they would fit - but when a switch box is very crowded with very thick stiff wires (and in this old home some have cloth insulation that is starting to come undone) then it would get gnarly (I felt like a cave man wrapping electrical tape around so many of those old wires) and with the occassional wire ends almost touching right where they go into the shelly - so I would end up putting electrical tape between the wires where they connect to the shelly’s afterward as well…
I did recently wise up and got both heat shrink tubing for the wires with the disintegrating insulation, and a ferrule crimping kit so I don’t have to worrry about forcing fat stuff into the shelly’s and trying to handle it by overtightening those screws. Live and learn… 
I moved to North America from Germany somewhat recently and have developed a love/hate relationship with how electrical systems are done over here. The great thing is that here our walls are mostly hollow and that makes it easy to fix stuff, the downside is that any electrical fire has a much greater risk of creating damage than it has in solid concrete or brick walls that I know from Germany.
Also my kettle takes 10 minutes to boil 1.5L of water. That took me 3 minutes in Germany. Oh the joys of 120V/15A vs. 230V/16A…
To add to that: Shelly devices were primarily made for the European market. I put some in my parents house in Germany, don’t actually have any in my house in Canada. Germany uses 1.5mm² wire (roughly 16 AWG) which may be why the terminals are a bit snug for the 14 AWG we generally use over here.
