Fire extinguishers are under pressure and may explode when combined with other materials.  They cannot be discarded with curbside garbage or brought to a Household Chemical Waste collection event.  Used fire extinguishers, smoke and carbon monoxide detectors can be dropped off at:

• International Fire Equipment in Lake Zurich 847.438.2343, 500 Telser Road. $5.00 charge per extinguisher (detectors containing radioactive material WILL NOT BE ACCEPTED) 
• Extinguish Fire Protection Inc., Wadsworth IL  847.693.9036  Extinguish Fire Protection is currently offering free pick-up service in the Lake County/Chicagoland area with no disposal fees.  Call to have them to pick up your unwanted extinguishers, smoke alarms and carbon monoxide detectors.
• Dependable Fire Equipment; 60 N. LeBarron Street; Waukegan, IL  847.662.8400 - No fees.

Most smoke detectors contain a small amount of a radioactive material. When installed in your home or office this material poses little threat but if broken open it can become a health hazard.  This is the reason that smoke detectors must be labeled as having radioactive content and their manufacturers must accept these items for disposal as hazardous waste.  
Homeowners can mail smoke alarms and smoke detectors back to their manufacturer by surface or UPS ground mail, marked "For Disposal" or contact the manufacturer by phone for instructions:
Manufacturer / Manufacturer's Address
Life Saver/Frynetics, Inc. 1055 Stevenson Ct. Suite 102 W. Roselle, IL 60172
Code One/Firex/Maple Chase 2820 Thatcher Road Downers Grove, IL 60515
American Sensors (800.387.4219)
First Alert/BRK Brands (800.323.9005)
Dicon 3334 Main Street Skokie IL 60076
Safety's Sake/Funtech 388 N Elliot Creek Road Amherst, NJ 14228