Catching answer to comment

Hello, I would like to ask, is there any function which let me catch the answer to comment? I know there is subscribe option to send email to person who get answer but I would like to catch the information and show notify bar.

For Example: Person 1 make comment and person 2 answer her. In this moment if person 1 subscribe to topic, is getting email, but I want just catch it and show bar.

Can u please somehow let me know which function let me catch the information about person who should get notify?