A computer was installed on the Le Verrier space station in the 38th century. Its functions included the locking and opening of doors.
At some point before the outbreak of the Sandmen, after a Maha Shivaratri/Oshogatsu/Christmas party, a crew member reprogrammed it not to allow any person entry to a room until they sang the song "Mr Sandman". The computer found it very amusing.
It was destroyed when the Twelfth Doctor disabled the station's gravity shields and sent it falling towards Neptune. (TV: Sleep No More)
Behind the scenes[]
The computer was voiced by Nikki Wilson, who was the producer of the TV episode in which it appeared. She said, in a behind the scenes video, that she was having "too much fun" doing the computer during the auditions, which led to her doing it on set.