Yes, carbon dioxide fire extinguishers. You can get them on ebay for ?5 - ?15 second hand. (I suggest you don't pay more than ?15 for one)
If you were wondering why one is black the other is red, they are both "The same" (2kg) except for age. Since 1997 all fire extinguishers have to be red, so if some one is telling you theirs is new and its black, its at least 14 years old.
EagleC wrote: ... but they will need to be refilled with "food grade" CO2. Industrial grade CO2 that they use for fire extinguishing is not as refined and can contain small quantities of toxic materials.
I have read about several people who have used them with no problems, which is why I thought I would mention it.