Material High Quality Plastic Size 70mm*27mm*7mm Application When traveling outdoors, it can help you confirm the location, avoid getting lost, find a partner, etc. Features (1) Made of high quality plastic, lightweight and easy to carry, easy to use.(2) The whistle has three holes, each hole sound is different.(3) The whistle is equipped with a hanging chain, which can fix the whistle for easy movement. User manualIt can be used for outdoor survival, training purposes. (In the wilderness in danger, survival in the desert, the whistle plays a big role! Although we have better communication equipment instead of whistles, but the role of the whistle still cannot be ignored. When modern equipment without electricity supply, signal shielding area, orientation determination, water danger, etc., appears when the whistle comes into play.)Below is the common whistle language● Short beep (within one second)■Long beep (more than three seconds)Whistle interval inside the command 2 - 3 seconds, interval between commands 30 seconds or more(E.g., sending commands repeatedly requires an interval of 30 seconds or more) ●●■ (Two short, one long) gather towards the whistle●■(One short, one long) exit, acceleration●■■(One short, two long) someone falls off the line, the front line is waiting for the back line●●●(Three short) seek help when you're in trouble●●●■■●●●(Three short, three long, three short) universal SOS code