The Crime Watchers Hotline  was a special hotline for Muggles set up in the summer of 1993, so that Muggles could report any sighting of Sirius Black, without compromising the knowledge of the existence of the wizarding world.  It was either run by Ministry of Magic wizards or the Ministry of Magic became aware of the calls the Muggles made to it.
Sirius Black was sighted in Dufftown, near Hogwarts Castle, sometime between 2 September and 31 October of 1993, by a sleepy Muggle woman. She called the hotline, which automatically alerted the Ministry of Magic's services. A special squad from the Ministry was dispatched to Dufftown, as were hundreds of Dementors, to the panic of the town's population. However, when they got there, Black was already gone. 
- Harry Potter and the Prisoner of Azkaban (First mentioned)
- Harry Potter and the Prisoner of Azkaban (film) (First identified as Crime Watchers Hotline)