I have one mounted on the firewall under the glove box.
Those little extinguishers don't last very long. If you've never had any fire training you might want to practice with one out in the backyard someday.
On some kind of schedule check the pressure gauge to make sure it hasn't leaked down and then turn it upside down and back up to help keep the powder loosened up. Also look at the nozzle opening. Several insects/bees have a habit of plugging up the nozzle.
