  We show that a single-Cooper-pair transistor (SCPT) electrometer emits
narrow-band microwave radiation when biased in its sub-gap region. Photo
activation of quasiparticle tunneling in a nearby SCPT is used to
spectroscopically detect this radiation, in a configuration that closely mimics
a qubit-electrometer integrated circuit. We identify emission lines due to
Josephson radiation and radiative transport processes in the electrometer, and
argue that a dissipative superconducting electrometer can severely disrupt the
system it attempts to measure.
