I would like to read and process the following:
1.) the state of existing switches e.g. door bell panel of a larger house
2.) the state of an binary error output of an older heating system.
3.) binary output for operating hour counter
All contacts are in different places without wiring.
I would prefer solutions without solder- even as I am able to solder 
… any ideas and brainstorming is welcome.
Have look to the Shelly Products.
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Thank you! I have checked it again and I found the Shelly Plus i4… sounds promising.
Hi, please review carefully the schematic/wiring diagram for the shelly plusi4 it is NOT a dry input device. The L1 of the input power is what it requires to “trigger” a state change on the 4 “digital inputs”.
edit
Shelly may have a equivalent of this
This however is a dry contact input device and if all you are looking for is the logic on /off state then it may be the way to go, and you just do not use the "relay contacts side of the device.
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@justaoldman Thank you for your recommendation!
Which binding do you use for the COLOROCK module?
The Shelly Plus i4 is available as DC and AC module.
And yes - I think both will deliver an voltage on the input - otherwise they could not detect the signal = state of the switch.
So may be I was wrong - the dry contact is always the output (relay / switch) the input always has a power supply.
In case of the modules from shelly or COLOROCK - I guess they drive out there own internal power supply?
But I wonder why I can find only rare information on this topic in the discussions
It seems also that there are not a lot of modules?
It seems a topic which is to easy 
yes I agree something so simple and basic that you would think should be a easy enough item to buy is really not,
The first device I listed you are correct the input control “switch” is a 3.3 volt dc level via a TTL input that gets pulled to an internal ground. It is most definitely NOT ISOLATED.
It uses a half wave series rectifier/regulator power supply that is derived from the input power. Since you said you did not want to solder anything this is the closest cheap approach if your binary driver is isolated it will be ok if it is not well then the genie will escape 
and you will not be happy, as it may not have the isolation you would need to directly connect it to a low voltage true binary control that likely referencing an earth ground as a logic low.
you should be able to utilize this binding.
many folks have reported it working well as one choice mqtt is the other way .
For me I use the ZigBee version of this switch device and it has been very reliable and very stable.
The other options are more pricey but you may be able to repurpose one of those garage door opener controls such as this one that has isolated inputs and may be more along the level of isolation your likely going to require. not sure what binding would work with this but here is one that is for sure isolated.
As stated, I have no idea what binding may work with this device honestly. But this one advertises it provides an APP and customizable /API that you could modify and maybe that is an good option.
Otherwise, I am afraid you will be breaking out the bread board and soldering iron to put some opto- isolators circuits together on what ever final solution you pick.
edit something like this basic opto-isolator circuit would be more then sufficient for driving any shelly or other device that the input is not potential safe. your digital output should be enough to forward bias the led and allow the pn junction to conduct and “close the circuit” , you may need to play with the 1k R10 value depending on the current of your logic driver source. and the GPIO output would connect to the shelly or other devices input to open / close its input switch however the shelly i4plus would NOT work for you with this additional add on circuit due to the use of Line voltage being sensed on the 4 inputs as a turn on/ off. think of everything on the output of pin3&4 is your shelly relay switch 1 plus or coloroc or sonoff or other device. And pin 1 and 2 are the logic outputs from either your door bell or heater . The pin 1 is the output logic line and the pin 2 is cold ground of your digital door bell or heater logic board and the pin 3 and 4 are actual switch contacts on the shelly device that open and close to initialize the devices on and off function.
one final note: I did see some premade opto-isolator circuit board on AliExpress and you can even find premade one on Amazon if you really do not want to solder
This and the colorock or even the sonoff zigbee relay switch would get you what you want.I also saw sonoff also makes a wireless version that you should be able to use the Sonoff binding as well to control it I think.
FYI For the shellyplus4i to work you would need to use something like the 4 relay version of this and add a 12 volt dc power supply to run the board.
Then use the relay dry contact here to drive the shelly4 iplus inputs. seems like a really hard way to get there just to use the shelly4i plus as a solution however.
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according to my knowledge Shelly 1 and Shelly plus 1 are the only dry contact modules from Shelly.
I would go for the Shelly Plus 1 as it’s the newer version and has a slightly better specification.
Then I know a zigbee switch from Livolo which has two dry contacts and a 433 Mhz dry contact modules from intertechno (guess it was its-2000). For zigbee and 433Mhz you would need the corresponding transmitter while Shelly is wifi that can be switched via mqtt or directly via the Shelly binding.
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From what I have tried and know The shelly 1 and Shelly plus 1 do NOT have isolated inputs they have dry contacts to control a output but the input is not isolated.
Perhaps that has changed now with the newer devices but in the past the input to trigger the device was not isolated.
OP is looking for a device to read a digital input logic level high/low condition and be able to action based on those changes.
Thus that requirement leads to needing a potential safe “isolated” input trigger port.
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Mostly folks are trying to control a device not read a devices binary logic state like you are doing the bulk of what they are readings the things like door switch’s magnetic contact open and closing the internal circuit or they are trying to turn an electrical appliances power on or off. otherwise, they are connecting to the device via some Api or other communication protocol and manipulating or consuming data from the internal control board of that target device.
@justaoldman @Larsen thanks a lot for your advise - I was able to refresh my knowledge about dry contacts and optocouplers 
I plan to enhance my openhab installation by two functions:
1.) Read the doorbell input and control the opener.
→ I would go for the Shelly plus 1
2.) Read two contacts from the heating control of the house:
- error (the most important)
- operating hours of the burner
→ I would go for the Shelly Plus i4 DC
As an option I would consider external Optocouplers from Amazon.