Facebook Groups Keyword Alerts

Hello.

Is there any tool, than can notify me, when on groups I will select and be a member there, some post with some keyword appears?

I am looking for specific listings on groups and I need to be fast, so I need some notifications or alerts that will help me with it.

These are not my groups, so I cannot use keyword alerts.

I don't think there is any ready tool available for your requirements. Better to hire someone for creating a custom tool if you are deliberately needed it.