A motion sensor in the porch would send an alert to a bleeper pager which could be carried by a carer in the house. The motion sensor itself is silent, so wouldn't cause distress to the lady when she is trapped in the porch. The bleeper pager would trigger continuously as long as motion was detected inside the porch. Alternatively, a door sensor could be placed on the inside front door. The door sensor is silent, but would send an alert to a bleeper pager which could be carried by a carer around the house.