I tried with the homewizard app the 868mhz smartwares pro (Cavius) smoke detectors and a 433mhz Flamingo FA21RF and both work fine when I set them in test mode, I got a push message from homey. It’s indeed not instant, in my case 2/3 seconds. The app polls every 10 seconds so if you are lucky it’s instant, unlucky 10 seconds.
Good job @Jeroen_Tebbens