Fox 40 Caul Fingergrip Whistle 8500-0008 in Black A referee and coach's whistle. The latest model from Fox, the 40 Caul Fingergrip . The latest technology used in these whistles makes them the most effective in their class. This model emits a sound power of +110 dB. The Fox 40 Caul has an elegant appearance, highly durable and comfortable rubber fingergrip . The whistle is packed in the original blister!