It's not easy when this happens. Basically alot of people don't realise that a normal car key actually CONTAINS three different layers of security.
1. The Metal Blade (We all know about this, it works like our house key).
2. The Immobiliser chip (This is a small passive glass chip embedded in the plastic part of the key. It's small, and features on all car keys made after 1995 (when the government made immobilisers compulsory). There is still a chip in a car key even if there are no buttons or battery.
3. The Remote Control Button Fob. (This fob is a the battery-powered unit with a circuit board and buttons which the driver uses to lock and unlock the vehicle and arm the alarm system if fitted. Most modern cars are supplied with this add on.)
4. Some of the very latest cars use a very different technology - keyless entry with no metal blade but i won't complicate this answer at this stage by going into detail.
When you lose your car key, the replacement will need to be physically "paired" to the vehicle - unless you have an existing key which in some cases can be "cloned" or duplicated.
This can either be done by your local Car Maker Dealership or by an independent Car Key specialist. You can find a list of specialists near you here:
http://www.yellowpage...york&q=auto+locksmith
I work for the leading Car Key specialist in London (
http://www.autokeysquad.co.uk ) BUT this company only offers roadside service in the UK.
You can find out more about car key technology here:
http://www.theaa.com/...ce/security/keys.html