  It is well-known that no local model - in theory - can simulate the outcome
statistics of a Bell-type experiment as long as the detection efficiency is
higher than a threshold value. For the Clauser-Horne-Shimony-Holt (CHSH) Bell
inequality this theoretical threshold value is $\eta_{\text{T}} = 2
(\sqrt{2}-1) \approx 0.8284$. On the other hand, Phys.\ Rev.\ Lett.\ 107,
170404 (2011) outlined an explicit practical model that can fake the CHSH
inequality for a detection efficiency of up to $0.5$. In this work, we close
this gap. More specifically, we propose a method to emulate a Bell inequality
at the threshold detection efficiency using existing optical detector control
techniques. For a Clauser-Horne-Shimony-Holt inequality, it emulates the CHSH
violation predicted by quantum mechanics up to $\eta_{\text{T}}$. For the
Garg-Mermin inequality - re-calibrated by incorporating non-detection events -
our method emulates its exact local bound at any efficiency above the
threshold. This confirms that attacks on secure quantum communication protocols
based on Bell violation is a real threat if the detection efficiency loophole
is not closed.
