[akkartik]

"The QHL is not depicted as being able to move itself; it is moved passively around its environment by riding on humans, air currents, etc. However, at least a bit of mobility is implied by the presence of a magnetic actuator and by the QHL’s ability to create a gritty surface on a switch."

The way I imagined this while reading the book was that the sensors are ubiquitous, so it's not about making them move so much as selecting the sensors in a specific area to view imagery from or enable grit attraction on.