OP is trying to detect a ring, not provoke one.
That’s why a relay makes no sense.
Why to waste 5v power supply and relay?
This is how I did it from my AC doorbell using optocoupler. AC doorbell to DC to 433mhz device My Doorbell used 18V and I didn’t fancy running a esp off it so I modified a 433 door sensor. It has worked well.
A very simple and safe way to detect electrical AC current in a wire is to use a “Current Switch” like the one linked below. You can then simply enable the internal pullup on the ESP8266 Digital GPIO pin, connect a wire from that pin to the dry contacts of the current switch, and then connect another wire from the ESP8266 GND pin to the other dry contact terminal on the current switch.
Someone else solved it simply by added a reed switch…
I had tried that but couldn’t get it to work.
I guess when you press a button on a doorbell, you want doorbell to ring. Shelly can do that. + you can easily detect when it happens.
Or you can put shelly in detached mode and do whatever you want to do in HA.
Or am I missing something here?
Did you look at the initial drawing?
It’s already ringing, and OP wants to keep it as it is.
@sri4iot Please don’t mark your wrong drawing as the solution. It will confuse future visitors of this thread 
I saw the drawing. I understand what OP wants to do, I am just saying there are other ways to do it. Perhaps he did not think of other possibilities, that’s all.
Then maybe I miss something…
Where would you put the Shelly in the picture?
You might have seen the you tube video I have linked, my door bell directly operates on 220-230V AC, not having any step-down transformer or DC conversion circuits. So in order to automate I need some kind of DC circuit that’s the reason I have a 5v Power Supply. I have seen other reed switch automation. However there are also cases mentioned those automation that there are false positive alerts. Since my door bell is just above my main door, if my kids shut the main door with a bang the reed switch may get triggered and you get false positive alerts. So I am thinking to keep the automation is triggered when someone is pressing the bell switch.
With respect to AC712, I have bought couple of them thinking similar to what you do have suggested. However if we go with any voltage or current sensor there will be some delay in getting the value sensed by the respective sensor, sending that to d1 mini’s A0 to detect the value is in range and then perform the automation. I am sure it will be in milli seconds and the d1 has to be refreshed accordingly. If you have any working example, could you please share the link so I can refer and proceed accordingly.
For me, the circuit I have proposed is working so the drawing is not wrong logically nor the yaml. Anyway, I have removed the marking as “solution”. I will wait for a better approach to solve this.
Ok, nevermind then. I thought you followed the optocoupler route.
I’m quite surprised that it’s working, tbh. Reversing the relay is … creative 
Unless I’m missing something, I think @Karosm’s suggestion to use a Shelly 1 is solid.
It’s a single component which can handle 240v and detect the doorbell being pressed.
No need for parallel circuits and requires less rewiring than what you currently have in your diagram. The best thing is, it will not interfere with the original bell functionality except in the case of a hardware failure.
Diagram below, just imagine the lamp as your bell
Not to forget that it’s certified product. Diy approach, even if well made, will never be.
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The only place I can get shelly in my country is via amazon. The price is almost double compared to the UK price. I know that link is showing 2 units but the cost is still double for a single unit. I will watch for any good deals on this and will go with your suggestion. Thanks a ton for helping me in this regard.
If you referring to India (based on your amazon link), Shelly themselves deliver to all countries, including India.
You can order direct from there here. Just make sure to select your Delivery country in the top right corner.
Precisely Shelly Plus 1 or Shelly 1 mini Gen3 or whatever 2nd or 3rd generation Shelly.
Thanks for sharing the model. The challenge with direct shipment from Shelly is, I will end up working with customs here once it reaches my country. I may have to do lot of paper works, etc. Since its a good to have automation, not a must to have, I can wait for the shelly to be available in the market or on Amazon.
If you don’t mind, if you/anyone is having spare shelly, will you be able to check whether it detects the bell type switch press and perform automation triggers? If I am right, most of the smart switches works with rocker type on/off switches but the bell switch will be too quick for it to detect the key press and trigger.