Physical termite barriers, like all types of termite barriers, are designed to prevent termites getting into a building undetected. A physical barrier does this by preventing them being able to access the inside of the building and forcing them out. To that end, the barrier may be connected to either a concrete slab, or it comes out to a visual inspection zone, as is illustrated in these pictures.
The pivotal thing about visual inspection zones is that they need to be clear of obstructions and easy to see. The Australian Standard (AS3660.1) as well as all barrier manufacturers recommend that a clearance of 75mm be available between finished ground height and the barrier.
So if your home or a home that you are considering buying has a physical barrier, then you may want to check that there is sufficient clearance around the perimeter. Making sure that there isn't anything covering it up, as the barrier cannot work unless it has been installed correctly, irrespective of the type of barrier used.
A physical barrier running into a step, for this barrier to work, it needs to be cast into the concrete step. It's important to check all these details. This barrier was not cast in, potentially allowing termites to get in undetected.