At liberty of advertising my own alarm system integration, I went down the Visonic Powermax route. It is not difficult to DIY the install as it is all wireless (though can be pro installed), counts as a Class 2 alarm system (from memory that was the right name for it) since it can detect jamming and support phone notifications and all sorts, has a few siren options, remote keypad/RFID tags/…
Plus with the integration I have got all of the sensors as separate devices in SmartThings and get notifications on state change (which then trigger photos to be taken on my CCTV etc etc). [RELEASE] Visonic Powermax Alarm