Safety Whistle EN394 ISO 12402-8.
The safety whistle is available as a multi pack on this link. You may wish to consider this option of a pack of 10 or 30 whistles.
It is designed as a safety whistle for lifejackets but has scope for much wider use such as walking, hill running and use by rescue services.
The whistle will attach by cord. It also has a hook that will enable it to sit on an elastic loop over the oral tube. It can be stowed on the UML Sea Flash Bracket, which is designed to stow both the Sea Flash Light and a whistle.
The Whistle is type approved ISO 12402-8. This specifies the safety requirements and test methods for accessories used for personal flotation devices (PFDs), with regard to the technical provisions of the International Convention for the Safety of Life at Sea (SOLAS).