I’ve had a ton of requests for this for konnected.io. It’s on our roadmap for next year to create a product that can support connecting a wired system “in parallel” with a functional traditional alarm system.
If you have some electrical engineering skills, you theoretically can do this now with my DIY Prototyping kit and some additional resistors or other components. Unfortunately it’s not something I can officially support or provide documentation for at this time, but I know others have done it. There’s some discussion in this thread:
You’ll all be the first to know when we have a “productized” offering to do this.