The scenes in front of Claudia's door were filmed in the same building as REC (2007), a movie from the same director.
Number #190 in Fangoria's Top 300 Horror Movies of All Time.
Carlos Lasarte, who plays the mad convict Santini in this movie, would later on star in Jaume Balagueró's movie REC (2007).
Though it received mixed reviews upon release, the financial success of this film has been cited by film scholars such as Antonio Lazaro-Reboll for launching Jaume Balagueró's directing career and marking the beginning of a series of numerous studio horror films produced in Spain, from Balagueró's subsequent film REC (2007) and J.A. Bayona's The Orphanage (2007), marking a "way of making films in Barcelona typified by quality genre production."