One of the most common first sensors people buy for their home is a motion sensor. But in almost all cases, you want a presence sensor instead. The one I'd want is the FP300, which Aqara released ...

It allows users to monitor room occupancy ... “The EnOcean EMDC energy-harvesting motion and activity sensor redefines smart building technology. It offers a streamlined solution for monitoring ...

This would mean they could automatically switch on when someone enters a room without using a separate motion sensor. Even better, the new functionality looks set to be added to existing Hue bulbs ...