  Many models of physics beyond the Standard Model predict minicharged
particles to which current and near future low-energy experiments are highly
sensitive. Such minicharges arise generically from kinetic-mixing in theories
containing at least two U(1) gauge factors. Here, we point out that the
required multiple U(1) factors, the size of kinetic-mixing, and suitable matter
representations to allow for a detection in the near future occur naturally in
the context of string theory embeddings of the Standard Model. A detection of
minicharged particles in a low energy experiment would likely be a signal of an
underlying string theory and may provide a means of testing it.
