  Future detection of high-redshift gamma-ray bursts (GRBs) will be an
important tool for studying the early Universe. Fast and accurate redshift
estimation for detected GRBs is key for encouraging rapid follow-up
observations by ground- and space-based telescopes. Low-redshift dusty
interlopers pose the biggest challenge for GRB redshift estimation using broad
photometric bands, as their high extinction can mimic a high-redshift GRB. To
assess false alarms of high-redshift GRB photometric measurements, we simulate
and fit a variety of GRBs using phozzy, a simulation code developed to estimate
GRB photometric redshifts, and test the ability to distinguish between high-
and low-redshift GRBs when using simultaneously observed photometric bands. We
run the code with the wavelength bands and instrument parameters for the
Photo-z Infrared Telescope (PIRT), an instrument designed for the Gamow mission
concept. We explore various distributions of host galaxy extinction as a
function of redshift, and their effect on the completeness and purity of a
high-redshift GRB search with the PIRT. We find that for assumptions based on
current observations, the completeness and purity range from $\sim 82$ to
$88\%$ and from $\sim 84$ to $>99\%$, respectively. For the priors optimized to
reduce false positives, only $\sim 0.6\%$ of low-redshift GRBs will be mistaken
as a high-redshift one, corresponding to $\sim 1$ false alarm per 500 detected
GRBs.
