  There is gathering indirect evidence suggesting non-conservative evolutions
in Algols. However, the systemic mass-loss rate is poorly constrained by
observations and generally set as a free parameter in binary-star evolution
simulations. Moreover, systemic mass loss may lead to observational signatures
that are still to be found. We investigate the impact of the outflowing gas and
the possible presence of dust grains on the spectral energy distribution (SED).
We used the 1D plasma code Cloudy and compared the results with the 3D
Monte-Carlo radiative transfer code Skirt for dusty simulations. The
circumbinary mass-distribution and binary parameters are computed with
state-of-the-art binary calculations done with the Binstar evolution code. The
outflowing material reduces the continuum flux-level of the stellar SED in the
optical and UV. Due to the time-dependence of this effect, it may help to
distinguish between different ejection mechanisms. Dust, if present, leads to
observable infrared excesses even with low dust-to-gas ratios and traces the
cold material at large distances from the star. By searching for such dust
emission in the WISE catalogue, we found a small number of Algols showing
infrared excesses, among which the two rather surprising objects SX Aur and CZ
Vel. We find that some binary B[e] stars show the same strong Balmer continuum
as we predict with our models. However, direct evidence of systemic mass loss
is probably not observable in genuine Algols, since these systems no longer
eject mass through the hotspot mechanism. Furthermore, owing to its high
velocity, the outflowing material dissipates in a few hundred years. If hot
enough, the hotspot may produce highly ionised species such as SiIV and
observable characteristics that are typical of W Ser systems.
