Smartdust is a hypothetical system of an unbelievably large number of tiny microelectromechanical systems (MEMS) such as sensors, robots, or other devices, that can detect, for example, light, temperature, vibration, magnetism or chemicals; are usually networked wirelessly; and are distributed over some area to perform tasks, usually sensing.

A typical application scenario is scattering a hundred of these sensors around a building or around a hospital to monitor temperature or humidity, track patient movements, or inform of disasters, such as earthquakes. Spread it across any areas where one wants to monitor activities and have the data sent via wireless networks to a headquarters where it is analysed and used in any way planned such as city planning or traffic prediction. In the military, they can perform as remote sensors to track enemy movements, detect poisonous gas or radioactivity.  Is it too small to notice? Should we be paranoid?

The ease and low cost of such applications have raised privacy concerns. The possibility that a ‘swarm’ designed to self-replicate and evolve to solve a problem might progress beyond our control has also raised safety concerns in science fiction stories, such as Prey
by Michael Crichton. See also self-replicating machines in fiction. This possibility comprises an end of the world scenario known as grey goo.