  Context. Gamma-ray bursts (GRBs) can be detected at cosmological distances
and therefore can be used to study the contents and phases of the early
Universe. The 4-150 keV wide-field trigger camera ECLAIRs to fly on board the
Space-based multi-band Variable Object Monitor (SVOM) mission, dedicated to
studying the high-energy transient sky in synergy with multi-messenger
follow-up instruments, has been adapted to detect high-redshift (high-z) GRBs.
Aims. Investigating the detection capabilities of ECLAIRs for high-z GRBs and
estimating the impacts of instrumental biases in reconstructing some of the
source measured properties, focusing on GRB duration biases as a function of
redshift. Methods. We simulated realistic detection scenarios for a sample of
162 already observed GRBs with known redshift values as they would have been
seen by ECLAIRs. We simulated them at redshift values equal and higher than
their measured value. Then, we assessed whether they would be detected with a
trigger algorithm resembling that on board of ECLAIRs, and derived quantities
such as T90, for those that would have been detected. Results. We find that
ECLAIRs would be capable of detecting GRBs up to very high redshift values
(e.g. 20 GRBs in our sample are detectable within more than 0.4 of the ECLAIRs
field of view for z > 12). The ECLAIRs low-energy threshold of 4 keV,
contributes to this great detection capability, as it may enhance it at high
redshift (z > 10) by over 10% compared to a 15 keV low-energy threshold. We
also show that the detection of GRBs at high-z values may imprint
tip-of-the-iceberg biases on the GRB duration measurements, which can affect
the reconstruction of other source properties.
