@bangali is correct there isn’t an out of the box driver called Motion Detector but there is one called Virtual Motion Sensor which should work for you. I use this in one of my apps. So try:
addChildDevice(“hubitat”, “Virtual Motion Sensor”, “alarmchildzone${curzone.zoneid}”, null, [name: thiszonename])
Also noticed a missing parameter in the addChildDevice function call where I am passing null.
