Scanner 4 : A radio receiver that automatically monitors several frequencies on a rotating basis and receives any signal broadcast; volunteer fire fighters often use them to receive fire alarms
Ralph W. Burklin & Robert G. Purington, Fire Terms: A Guide to Their Meaning and Use, National Protection Association, Boston, MA 1980 USA. (Guide: Meaning and Use, Nat Prot Association Fr Srvc - Amer) {457}