whistle

Fox 40 CMG Whistle with Cushioned Mouth Grip - Black
$6.99
I have ordered 4 of the Fox 40 whistles w/mouth guard. It really helps as it is easier to hold in your mouth and keeps you from bitting down on the standard whistle plastic mouth piece. When you blow a whistle 200-300 times in a match it is a lip saver.

Kwik Tek W-2 Whistle With Lanyard (Red / Black)
$4.50
I got this as a gift so I can't claim firsthand knowledge of its quality. But the person I gave it to said that she feels safer working a night shift with it clipped on her belt when she goes home. The whistle is loud and the clip allows the user to have it handy for possible emergencies.

Spalding Whistle
$2.99
well it's a whistle... and it works... if you're considering purchasing this as an emergency whistle try finding one without the pea inside, if you're in a freezing environment they can stick and render your whistle useless.

Mikasa WH-5 Pro Volleyball Whistle
$2.59
I bought a couple of these whistles, and must say I am disappointed. The shape of the whistle, this may not be clear in the photo but it is J shaped, seems to point the sound right back towards the whistle-users ears. I was almost stunned when I gave the whistle a big blast. Yes, the whistle doesn't cost much, and in this case you get what you pay for.