Our 4mm 3D printed whistle is very loud and compact! This whistle is good to spread awareness just in case you are in any dangerous sitiuations. It also a keychain loop to put on a lanyard or your collection of keychains. Other colors are available Basic Blue, Green, Red, Orange, Black and white are $1 Metallics are $2 Fluro Green (coming soon), Marble white, translucent