Assorted Colored Siren Whistles PKG (5). Vrooom! This well-made plastic siren/whistle, a touch over 3/4" in diameter and a similar touch under 2" long, has a perforated metal disk that rotates in response to a silent blast from the perpetrator's lungs. This creates a high-pitched, loud and certainly distinctive siren-sound that picks up pitch in relation to the air velocity, sustains it as long as your wind holds out, and winds down quickly thereafter. A fine way to signal your arrival or departure. Probably not loud enough to collect the clan at the beach, but loud enough to get their attention in the classroom! The size makes it hard, but not impossible, to swallow, so please use care in teaching youngsters to sound like a miniature air raid siren.