  We study the scalar radiation emitted by a source orbiting a
Schwarzschild--anti--de Sitter black hole in circular geodesics. We obtain the
emitted power using quantum field theory in curved spacetimes at tree level
with reflective boundary conditions at infinity. We compare our results with
the ones obtained in Schwarzschild and Schwarzschild--de Sitter ($\Lambda > 0$)
spacetimes. In the Schwarzschild-de Sitter spacetime we observe an enhancement
of the emitted power associated to the lower multipole modes, when compared
with the Schwarzschild case. In contrast, for the Schwarzschild-anti-de Sitter
spacetime, the enhancement is rather of the higher multipole modes.
