You sit down at the bar and order a double Scotch and soda. But the drink tastes more like water than Speyside malt. No worries, just whip out this trusty alcohol tester and catch that 250 lb. bartender red-handed. You hold up your multicolored testing device and shout: you, sir, are a cheat! What happens next is anyone's guess, but I hope you are wearing running shoes.
Of course this is also ideal for any serious bartender or drinking business. The principle is based on the different weight of alcohol and water. The position of the rings and the colors show the percentage of alcohol to water. It comes in various materials and with different numbers of rings for measuring.