I would like to install an anti-intrusion alarm.
For security I think would be better to have something that works independently from home assistant. At the same time it would be nice to read the alarm status or arm/disarm from home assistant.
So basically I would like a system that integrates to home assistant but home assistant is not required.
I saw some brands like somfy, ezviz, ajax, etc, but not sure which one can work well with HA.
Do you have suggestion?
Use an off the shelf basic alarm system or use Home Assistant running off a UPS with Frigate cameras / real person and occupancy detection and numerous sensors across the house ?
Let me think which is better ? 
BTW one serious question - Will the anti-intrusion alarm work and record throughout a power cut ?
EDIT: Maybe start here ? Integrations - Home Assistant
I think, as a minimum, an alarm system should work on a powercut and should have a backup simcard.
The reason for not having HA in the middle is simply that is a more complex system and complexity brings an higher probability of failures (E.g. sensor incompatibility after an updare, hw problems less probable on embedded systems with a single purpose, automation bugs etc)
I ll have a look at the list of integrarions, thanks