Not sure if this is the correct place to post this but it sort of makes sense. Please move if you feel it does not belong here.
I have not seen a good demo of how to wrap a key with foil, and since we are on the internet where what one person types may not be what others read (lol) I figured I would post some photos we can all link back to in other conversations when the need arises.
So basically this test will determine if you have a Radio Frequency (RF) based immobilizer system, without taking your dash apart.
This does NOT mean that if the foil has no effect on operation of your car that you do not have an immobilizer system. It just means that your car does not have an RF based system, or has multiple systems.
Please refer to your owners manual for your car or ask one of the helpful people here to verify what type of system your car has.
Also please note that it could be possible on some GM applications to accidentally set your vehicle into tamper mode. Consult with your owners manual on how to get your vehicle out of tamper mode if this happens.
First an RF based key will typically have a larger plastic head (the part you hold onto while turning the key). This is a ca. 2007 GM key and is just shown as an example.
You want to lay the aluminum foil shiny side away from the head of the key, and poke the key through the foil. Being careful not to make the hole too large.
Carefully wrap the foil around the head of the key completely sealing the head inside the foil. Pay attention to where the blade poked through as to not tear the hole larger while wrapping. Also make sure the foil does not extend too far onto the shoulder of the blade indicated between the two red lines in this photo. A large clump of foil may make inserting the key into the cylinder difficult.
Take a look at the key from this angle. You should not be able to see anything but the metal blade itself. Carefully seal the entire head of the key especially from this angle. Any gaps on this end can nullify the test.
Keep in mind this thread is meant to be an aid in other conversations that should have more specific information about its use on your vehicle. Do not attempt this test without first consulting your owners manual and a helpful 12v professional. To master and control electricity is perfection. *evil laugh*