Hi
I am using ESP8266 as output 3.3 vdc and the other controller input must be volt free input can optocoupler help me in this case or need another way?
Can you explain what volt free means?
Can you tell about the input that needs to be controlled from your esp output?
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Maybe a hand drawn wiring diagram would help.
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The specs for input:
Accept maintained inputs and momentary inputs
with 40 msec minimum pulse times
Off-state leakage current must be less than 100 µA
Open circuit voltage: 36 V- maximum
Inputs must be dry contact closure, solid state,
open collector, or active-low (NPN) / active high
(PNP) output
– Open collector NPN or active-low on-state voltage
must be less than 2 V- and sink 3.0 mA
– Open collector PNP or active-high on-state voltage
must be greater than 12 V- and source 3.0 mA
Inputs must be dry contact closure, solid state,
open collector, or active-low (NPN) / active high
(PNP) output
Is my understanding correct that it can be either dry contact closure or solid state or open collector npn or open collector pnp?
Yes. Could optocoupler solve it?
It's perfect 
Only restriction: NPN output transistor requires switched positive voltage at collector, negative voltage at emitter.
The opto coupler would do just fine. The emitter goes to ground, the collector to the input terminal. You can use the output of the Arduino to drive the LED, you will need to add a resistor in series. Do not connect the grounds of the Arduino to the controller, assuming this is the only connection to the Arduino..
I am thinking to use this I can use input from esp8266 to drive the led and GND and output to 3rd party controller input?
Your specs says that the voltage at the other side can be 36 V....
24V opto coupler device is likely to not survive...
I think means can handle max 36 v 
The open circuit voltage is produced by the receiving side. You do not have influence on that value.
Your proposed optocoupler should be able to wtithstand 36V (and some more to be on the safe side).
But it is up to you to find other meanings of your own words on the specs. Be carefull: optocouplers do not care about your meaning, they care about their experienced reality...
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you are right in open circuit voltage max 36v.
the specs of optocoupler:
Parameters:
- Input signal voltage: 3-5V/12V/24V (optional)
- Output signal voltage: wide voltage, suitable for DC1.8V-24V
- 817 features:
Isolation voltage greater than 3000V
Input current up to 50MA
Working current>1MA
The maximum output current is 50MA (the input current must be 15-20MA)
In 3rd party datasheet 36 v is for miswiring protected only!
• Input is miswire-protected up to 36 V-
Spec 2 says it is not suitable for 36V.
I strongly doubt if that board in your picture can provide isolation of 5000V.
The input resistor should have been to the left of the opto coupler. Instead it is close to the output...
Just tell us what this device is and post the datasheet here.
Maybe someone here has actually used one, whatever it is.
You can simply measure the open voltage...
Meten = weten (dutch for to measure = to know)
Is this the door sensor switch?
Connection to XOR circuit?
the specs for Contact closure input 3rd party controller:
Programmable Wiring (IEC PELV/NEC® Class 2)
• The attached device must provide a dry contact
closure, solid-state output, open collector or activelow (NPN)/active-high (PNP) output.
– Open collector NPN or active-low on-state voltage
must be less than 1 V- and sink 3.0 mA
– Output collector PNP or active-high on-state voltage
must be greater than 12 V- and source 3.0 mA
– The outputs must stay in the closed or open
states for at least 40 msec in order to be
recognized by the DALI® Power Module
• If there is any question as to whether the third-party
device generating these outputs is compatible with
these specifications, contact the manufacturer.
• Input is miswire-protected up to 36 V-.
my ESP8266 output is 3.3 volt and should make it as dry contact to be work with input 3rd part controller.
I was thinking optocoupler can handle the case here or really need a relay work with 3.3 volt?
it's part of it but this is the receiver of signal from sensor switch.