About the whistle:
With a thickness of only 3 mm, the flat whistle fits in any wallet. Despite its
flat design, it’s really loud. It is also possible to wear the whistle as a chain
or attach it to a keychain.

Sound:
It has a clear double tone. Due to the size, the sound is quite high. But it is
enough to get attention.

3mm – 34m-1.74g-15%

(LxWxH)-21x41x3mm

4mm – 58m-15%

(LxWxH)-28x54x4mm

5mm – 1hr33m-15%

(LxWxH)-35x68x5mm

Attribution goes to https://www.printables.com/model/495173-flat-pocket-whistle