Alarm systems are often unnecessary. However, if you need one, I’d go with an old-school hard-wired system from a company like DSC. I’d avoid any “smart” devices unless you really want the convenience. For cameras, you can get a real CCTV system with beefy cameras that record to a local hard drive.

Wireless systems, like Simplisafe, are hilariously easy to bypass with even a weak radio transmitter. The devices run on very low power so put out weak signals that are easy to drown out.

Security companies will try to charge you insane monthly fees for crap you don’t need. There are companies out there that will tie into your wired system and do things like call you and the police when things go wrong for less than $20/mo. If you want the police to actually respond, I’ve heard you’ll need a camera system, otherwise they’re going to assume it’s a false alarm and get to it when they get to it, if ever. Any additional upgrades, like connecting additional smart devices to a security app managed by your provider, are generally scams imo.

Once you add networked connectivity to any of this, they tend to lock things down so they can charge you unnecessary fees to access your devices. The nice part of a dumb wired system, besides being unhackable, is that you can wire an esp32 up to it yourself and connect it to home assistant. I’d check for device compatibility with esphome before buying anything.

That’s all for actual security, though. It’s going to be overkill for 99.999% of people. The convenience of smart and/or wireless devices should not be overlooked. For something like windows, a few zigbee contact sensors from Aqara would have you covered for very cheap and the install is just sticking them on. I wouldn’t consider it a true security system, but it’s easier and more realistic. Throw in a smart camera and doorbell and you’re golden. Eufy lets you store video locally without a subscription, which is nice, but that doesn’t actually mean that it’s private.