Star Trek: Deep Space Nine

It has been established in many other episodes of the Star Trek universe (including Deep Space Nine) that the transporter technology has numerous built in safeguards against weapons and/or uninvited guests. None of which were triggered when Mirror Bareil beamed onto the station's Central Operations transporter during a time of war. Even if the automatic systems were somehow disabled, there was enough time to set up a force field to contain the subject until an identification could be made.

Sisko has security clear a path to Landing Pad A to allow Mirror Bareil and Kira to depart. The landing pads are in a bay above the habitat ring, as shown in Emissary. However, the outside shot shows the runabout docked at a pylon.

Given the history of other Mirror Universe inhabitants coming through the main transporter pad in ops, without a ship present, it doesn't make sense why, after detecting Antos coming aboard, to have met him without an armed guard.