(at around 25 mins) When Specs and Tucker analyze the footage of young Josh, the "Panasonic" VCR logo has been worn away in places so that it reads "Panic" instead.
The hospital featured in the film (Linda Vista Community Hospital) has featured in over thirty movies--mainly horror films--many TV series and also music videos.
There is an Australian flag in the corner of Dalton's room in the Lambert house. Leigh Whannell (Specs, writer of Insidious (2010)), Rose Byrne, Angus Sampson and James Wan (writer and director of this second film) all come from Australia; however, Wan was born in Malaysia, but later moved to Australia.
(at around 22 mins) When Specs and Tucker enter Elise's house, there is an African Tribal painting hanging on the wall. It is the same painting seen hanging in Daniel's study in Paranormal Activity 2 (2010) and in the Grandmother's house in Paranormal Activity 3 (2011).
A majority of the film was shot inside Linda Vista Community Hospital, which also doubles as the abandoned hospital that the characters visit.