  The operation at the Z-pole of the FCC-ee machine will deliver the highest
possible instantaneous luminosities with the goal of collecting the largest Z
boson datasets (Tera-Z), and enable a programme of Standard Model physics
studies with unprecedented precision. The data acquisition and trigger systems
of the FCC-ee experiments must be designed to be as unbiased and robust as
possible, with the goal of containing the systematic uncertainties associated
with these datasets at the smallest possible level, in order to not compromise
the extremely small statistical uncertainties. In designing these experiments,
we are confronted by questions on detector readout speeds with an extremely
tight material and power budget, trigger systems with a first hardware level or
implemented exclusively on software, impact of background sources on event
sizes, ultimate precision luminosity monitoring (to the $10^{-5} - 10^{-4}$
level), and sensitivity to a broad range of non-conventional exotic signatures,
such as long-lived non-relativistic particles. We will review the various
challenges on online selection for the most demanding Tera-Z running scenario
and the constraints they pose on the design of FCC-ee detectors.
