You have to unwrap it before you throw it, plastic makes crinkling noise
I've used about 2 or 3 of these over the course of a year, and I've seen two more go off in addition to those that I've thrown. Let me tell you first that this is an awesome grenade. With over 10 ounces of paint inside of it and because it goes off every time, it's quite reliable when it comes to eliminating your opponent. The only problem that I found was that you have to take off the plastic right before using it (I learned that the hard way) which may make a crinkling noise, thus giving your position away if your hiding. Other than that, it's awesome.
Definately a good buy, $6 may seem a little high, but it's a good sacrifice for its reliablility.