How to know if watch is in an activity, when in the Background?

Hello,

Somehow, I need to check if the watch/user is running an activity on the watch, while being in the Background service. I'm sending alerts with the background service to the user, but I want to pause them during activities, as that is annoying and unneeded. 

Is there a way to check this? I did not yet find a way to do this.

Best regards,
Wim