Trigger needed to detect a string status going from 'on' to 'off'

Hello, I must be missing something, maybe brain cells, I can not seem to find a flow addon that follows the following pattern.
Detecting a state change of a string from 'on' to 'off' or in fact from any string to another string. Can anyone please point me in the right direction.

Thank you

You don't need a "addon" for this, as it is at the core of node-red.

I would highly recommend to watch this complete playlist to get an understanding of all the basics, it will take at most an hour of your time but it covers all the concepts.

The filter node is what you use to observe changes. The switch node can then be used to route messages.

Your node > filter node > switch node

Further to @Steve-Mcl post, you can also observe changes in a switch node using != previous value