when you activate hads before landing the tardis checks the area to see if there is hostile action near the area its going to land at or if guns are being shot, the tardis will make some kind of noise wich will mean that you cant land there unless the guns arent being fired for 20 seconds or if teh hostile thing has left the the raideus and maybe the tardis takes off when a weapons is fired near the tardis or the tardis auto locks the door so even someone with a sonic cant get in