They come in a broad range of sizes, weights, and fire retarding agents. To help you choose the right equipment for your needs, it helps to familiarize yourself with different types of fire extinguishers.
You can get water-filled extinguishers that must be pumped up or operated with a pressurized air canister. But they are heavy, and hard to find, and effective only on fires classified by Underwriters Laboratories (UL) as Class A (wood/cloth/paper/some plastic). Hardware and department stores stock dry-chemical extinguishers containing flame-smothering, nonconductive monoammonium phosphate powder that will extinguish fires of Class A, Class B (flammable liquids such as oil and gasoline), and Class C (electrical). They leave a messy residue of caustic powder, however.
An A/B/C extinguisher is best; you don't have to classify a fire before putting it out. For kitchen fires, you can get a B/C extinguisher containing sodium bicarbonat—or keep a box of baking soda handy at considerably less cost.
Halogen fire extinguishers are more expensive but come in small canisters that are easy to carry in a vehicle or on a belt clip. Halogen, a universal extinguisher, is best for fires in sensitive electrical or electronic equipment, as it is noncaustic and leaves no residue. However, halogen gas is suspected of contributing to depletion of the earth's ozone layer and should not be used indiscriminately. Extinguishers are also rated for size, capacity and discharge duration, indicated by the number 1, 2, or 3 preceding the A and B class ratings. The Kidde Fireway 340s is UL-rated 3A:40-B/C and weighs eight pounds. Their $40 cost is negligible compared to the lives and property they save. A 1-A:10-B/C extinguisher has a quarter or less of the capacity. But because most of the tangible value is in the metal canister and plastic valve mechanism, it doesn't weigh or cost much less than the larger models. Better too much capacity than too little. Get the largest extinguishers you can handle. The big ones come with a gauge and are rechargeable.