Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
Whistle (company)
Whistle began experimenting with the SigFox internet of things network for its devices in May 2014. In January 2015, the company acquired Tagg, a competing startup based in San Diego, for an undisclosed sum for its battery life and location-tracking intellectual property, and Tagg's CEO, Scott Neuberger, joined Whistle. Tagg had started as a Qualcomm subsidiary in 2010 and released its tracking device one year before Whistle. By 2015, Whistle had distributed 100,000 devices and had about 40 employees.