Light + Sound
Bright lights are used to increase visibility in public and semi-public spaces, while different coloured lights are used for a number of reasons.
Blue lights are installed in some restrooms to make finding a vein difficult for intravenous drug users.
Pink lights are reportedly used in the UK for their calming effect and to amplify the acne (and resulting social discomfort) of loitering youth.
The Mosquito, a device that emits an unpleasant sound at a frequency only young people could hear, was spotted in McGill Parkette, close to Yonge and Gerrard in Toronto last spring. The anti-loitering device was removed after its use made media headlines.
Classical music is played from the overhead speakers in some Toronto Public Transit stations located close to secondary schools. This "uncool" music is thought to repel gangs and disperse gathering students.
Image source: http://www.movingsoundtech.com/