I call this the "dead man's switch" because it's where you want something to take action based on inactivity instead of activity.
Just to clarify, are you looking for an alert when there is no activity on the
lead or no activity in the
campaign itself?
In either case, here's the approach I'd take, there could be other methods that work too, but I have found this approach gives a good amount of flexibility on criteria.
EVENT - lead is created
--> Trigger your main campaign
--> Triggeryour alert campaign
Alert campaign flow steps would be:
- wait for [x] [hours/days/weeks]
- send alert
At the same time you have another triggered campaign listening for whatever activity it is you are monitoring for -- whether that is web page visits or the particular flow step in your given campaign that you want to be notified about the absence of.
Smart list trigger: [whatever event/activity you are monitoring for]
Flow step: remove from flow [your alert campaign]
Essentially this is creating a parallel flow to the main campaign you want to monitor that will send out an alert as the default condition. If the activity you are monitoring for occurs, the lead will get removed from the alert campaign and no alert is sent. If it does happen, keep them in the flow and send the alert.