Is there an option out there for people who want window and door sensors, and a smart hub you can use to set the alarm from? Possibly including an app? I'm looking for something where I buy and maintain all the equipment myself and DO NOT have to pay a monthly fee. Just like my security cameras where I bought the equipment and can use the Reolink app anytime to check them. Does this exist and if so who has the best product? My search has left me finding only products that make you sign up for their monitoring service.

Any zwave or zigbee set should work. Smartthings is a hub and app you can use for notifications.

You can DIY and scale a Honeywell Vista 20P build and then use an EYEZ-ON board to access and self monitor via the internet. Lots of info out there on this setup.

Honeywell Vista 20P, a real alarm system, a system capable of meeting U.L. requirements for alarms.

Use with an Eyezon Envisalink board.

Check out Bounder97 on youtube (10 - 12 part Vista 20P series) or myalarmguy.net for the basics.