This is good advice @DPittman. What he is saying is cheap to make and Uber reliable. I'm happy to draw a schematic for you if you are handy electronically. It's really a handful of components around an SCR and a relay. Drawback is there will be no indication which door or window is compromised without some fancier components. If what you want is as simple as this, I could build it for you with spare parts and a case. Lots of alarm systems in the 1970s used the same principle he is talking about: everything wired in a loop. Not fancy but reliable.I'm gunna break the mold here for this one.
I built my own alarm after I was broken into once. It's never happened again since but there have been a few attempts. Custom alarms have the advantage that a thief can never know how to defeat them. I built my own panel with smarts very similar to what you could do with an Arduino today.
And I'd bet they do make a panel like you need, but for this case, why not just go real basic - just for now at least?
Just wire all your switches as either normally open or normally closed through one low voltage supply and grounds to activate a relay. Or use several relays that close or open with the low voltage to trigger the siren. And use a key switch to turn the whole thing on or off. Just a plain old basic no smarts alarm that no thief would ever expect.
And here is a another tip that others might find useful too. Run a monofilament fishing line "trip wire" in a curtain to a pull switch and forget about glass sensors or regular window switches. They are too easily defeated. The curtain has to get pulled aside to get in and off goes the siren.
My shop and house today are monitored and I also have inexpensive Toucan wireless cameras that notify me when something is amiss.
Edit - The insurance discount pays for the monitoring service.