homeassistant

Most security systems these days are just whitelabeled zwave etc sensors with a proprietary hub and a monthly charge.

The nice thing about HA is that you can pull almost everything into it and then add whatever automations you want. Recent example was my SO complaining about how dark it was going to the car when they leave in the morning. Super easy to set up an automation that turns on the floodlight switches when the front door opens between dusk and dawn. All kinds of stuff like that that's really useful.

I only tend to dabble, but I have Home Assistant set up - one example I'm on a flexible electricity tariff which is based on wholesale prices. It chages every 30 minutes. I have an automation that grabs tarrif info. If the price goes below zero (which it does sometimes when the grid has more energy than it knows what to do with, my hot water heaters all automatically turn on.

You can definitely have all the gear and not need it. I've set mine up a little at a time to do specific tasks. Some examples:

Alert me if my side gate is unlocked at night, because that is the access to my business.

Check if there is water in the chicken house reservoir, as that means the chickens have dropped a pebble in the valve again.

More cost upfront, but as we've seen time and time against companies will start charging subscriptions for thing they previously didn't.

Then there'd the privacy benefits. Not needing to rely on some company to keep servers alive. Being able to more easily troubleshoot/upgrade/swap individual parts. Not having to use a different app for basically every single device. All that sort of stuff