Due to the extreme number of creatures passing back and forth between worlds, particularly after that which we call Event-X, it is virtually impossible to prevent the transit of anachronistic artefacts.
That said, as soon as one is discovered on [alt]Earth the Department attempt at least to record its existence and assess any dangers it may pose.
It is rarely necessary to remove anachronistic artefacts, particularly when they are from the past, and these assessments are usually brief.
Occasionally, however, such artefacts may cause localised disturbances–most frequently the Oz-Effect. These objects are confiscated out by the Department and stored or disposed of in line with procedures (see Storage of the Sacrosanct).
There is large black market demand for future-tech, with customers ranging from scientists to military forces and even large multinational corporations. A considerable amount of future-tech is likely already in use.
Michael Scott Hand 