Hi everybody 
I’ve asked Homey if they now have a date for such a direct integration with Homey. They confirmed me their R&D department is working on direct integration with Smart Home systems, but they do not have terms of its implementation. So I guess we’ll still have to wait … 
Earlier in this thread I mentioned someone made an integration of the SIA protocol in Home Assistant. So someone else forked this project and owns an AJAX alarm system: https://github.com/eavanvalkenburg/sia
The installation was quick and simple in Home Assistant. After that I made sure HA made URL calls to Homey when the alarm is on or off. In Homey I created a virtual alarm device to react on these calls. I now have a working on and off state in Homey. Very basic and simple, but at least I can now integrate the arm and disarm states of AJAX in my flows.
@Earl_Grey does this app work fine with Google Nest ? Sorry if it’s a “stupid” question, but I do not have any Google Home nor Mini for the moment, so I don’t know how it works !
Otherwise, the Ajax team explained me sending signal about status armed/disarmed is possible with Ajax Relay and wired contacts, but I prefer byuing a Google Nest instead of an Ajax Relay if this solution works fine 
