When the garda (policewoman) calls to the door, some of her walkie talkie chatter can be heard. This is in an American accent which would not be the case in Ireland. The piece heard is in fact a standard foley effect of an American police officer speaking on the radio and is often heard in TV and film.
The layout of Pierce's flat internally does not match the exterior shots. From the outside the garden level door is under the main steps to the house and would face the party wall with the next door house. On the inside the corridor from the front door has room on both sides, whereas it could only have had rooms on one side.