There was a fourth guard called Mr Smith who was a corpse sitting in the office. He had died three years before and the rest of the guards were dividing up his pay packet.

Source: IMDB

There is a security camera installed in the staff room in Episode One.

In Episode One 'Moonlight Becomes You' there is a book on the table of the office Carter and Sawn look in. The book's title is: Taxation.

Carter's, Bell's and Sarge's security number as seen on there blazers is all the same. It's 3.3.3.

The three security guards only use second names when addressing each other. We do not know Carter's, Bell's or Sarge's surnames.

Bell's nickname as given to him by Carter is Ding Dong.

The dead security guard Mr Smith has a daughter who lives in Australia.

A script written for series two never made it to screen and it involved Mister X, a legendary security guard who was idolised by the trio and so good at his job nobody had ever seen him.

Source

Exterior shots of the office building the trio are working at are located on Paradise Circus in Birmingham City Centre.

A US remake titled In Security was piloted but never commissioned in starred Trevor Eve.

Although the first series aired in February 1990 it was three years before the follow-up series was given the go-ahead. The long delay was prompted by Channel 4 executive Seamus Cassidy who was not happy with the proposed scripts for the second series.

Carter's accent changes from series one to series two. In series one he's speaks with a soft cockney accent yet in series two his accent become more northern. It has to be noted that during series one and series two Robert Lindsay who plays Carter was playing Michael Murray in G.B.H. who's character was quite clearly from the north of England.

In the episode Trouble in Mind both the Sarge and Carter are seen holding up a paper called the Catwell Gazette. Catwell is in Taunton, Somerset.

The security firm the trio work for is called 3.3.3. Security which is the reason they all have 3.3.3. on there blazers.

They work a twelve hour shift from 7pm to 7am.

Sarge is a Pieces.

Bell has a dog called Duncan who is an alsatian.

The 20th floor is the roof of the building and the highest level in the building.