Any good recommendations for a door alarm?

Dad likes to go outside sit on the porch and watch neighbors on the street and hopes they say hi and talk to him. Social guy all his life has been cut back with his dementia. Theres no telling if he'll walk over to their house to talk to them. Mom needs to be notified and alerted when he goes outside, whether it be the back yard or front porch. Need a good recommendation for a reliable alert for both doors when he opens the door. Have any suggestions?