  By analogy to Jovian radio emissions powered by the electromagnetic
interaction between Jupiter and its moons, we propose that close
magnetic-nonmagnetic white-dwarf pairs and white-dwarf planetary systems are
strong radio sources. A simple model is developed to predict the flux densities
of radio emission generated by a loss-cone-driven electron-cyclotron maser. The
radio emission from these systems has high brightness temperatures, is highly
polarized, and varies on a periodic cycle following the orbital rotation.
Masers from magnetic-nonmagnetic white-dwarf pairs, with orbital periods <10
min, are expected to be detectable over a wide range of radio frequencies.
Terrestrial planets in close orbits about magnetic white dwarfs, with orbital
periods $\la 30$ hr, can also produce detectable radio emission, thus providing
a means to identify Earth-sized extrasolar planets.
