remote alarm

My dad who is in the first stages of Alzheimers is going outside at night. That's not so bad really (at least at this stage) but I think that he's doing it because he's turned around in the house. I need an alarm that wakes me up to know when he's done it. I'm afraid that he will get outside and become even more disoriented. It needs to be something that will "alarm" in my room and not at the site. Home Depot doesnt' have such a thing. The alarms that the patients wear won't work because Dad doesn't see that he has a problem. So he won't wear it. Has anyone heard of such a device?

Anne