I installed an internal system with cameras, motion sensors and door sensors. They worked via a hub connected thru WiFi. I could control it thru my iPhone. It would alert my phone if a sensor was triggered.

I bought simple magnetic type alarms from Amazon, about 5$. They were two part, one on the door, the other on the door jamb, attached with sticky pads. They had a manual on off switch. They were plenty loud enough and served us well.

Here are a couple other ideas:
You could hang a string of bells on the doors say on the handles. Bedroom and front door. I used a Christmas wreath hanger.
Similar to a security door jam bar, use a rubber doorstop on the front door.
I switched to a Ring doorbell which even triggers when my screen door is barely opened.
Good luck

Try visiting a website called - unforgettable. They have a small catalogue of dementia aids to help make everyday life a little easier. Hope you find what you need. X

MIL doesn’t wander much and little strength so out of house escape is not a concern for us. BUT ... she is teetery at best with walker and at night a couple 3 years ago she fell and cracked a rib. Soo we have a bed alarm which is a pad and the alarm is NOT in the room with her but in our bedroom so if she gets up we know right away. We have a baby monitor in her bedroom and carry the portable with us or in same room with us. During the day we have a chair pad alarm and that one does ring where she is but we figure she’s awake so no scare factor.
Hope this helps