“Scary Movie” topped theaters with a franchise-best debut as low-budget hits “Obsession” and “Backrooms” continue to outshine bigger-budget competitors.

The U.K. and Ireland box office experienced a highly competitive frame as Paramount’s franchise revival “ Scary Movie ” secured the top spot, debuting to a robust £4.1 million ($5.6 million).

The new movie is tracking for a franchise-record opening of approximately $52.7 million, well above the previous high set by Scary Movie 4 in 2006, from 3,490 theaters, on a reported budget of just $3...