Fire sirens are often called "fire whistles", "fire alarms", or "fire horns". Although there is no standard signaling of fire sirens, some utilize codes to inform firefighters of the location of the fire. Civil defense sirens also used as fire sirens often can produce an alternating "hi-lo" signal (similar to emergency vehicles in many European countries) as the fire signal, or a slow wail (typically 3x) as to not confuse the public with the standard civil defense signals of alert (steady tone) and attack (fast wavering tone). Fire sirens are often tested once a day at noon and are also called "noon sirens" or "noon whistles".