What Car Thieves Don't Want You to Know

Ex-con Steve Fuller, who has been convicted six times for stealing cars, has decided to reveal all to make amends for the hundreds of cars he stole in the past.

Fuller outlined to ABC News' 20/20 program what car thieves look for, what they know that we don't, and how you can best protect your beloved vehicle. Here are five of his tips:

1. Be careful where you park
It might sound obvious, but Fuller recommends avoiding dark locations, including carports, underground parking and apartment complexes. Of the latter, Fuller said that it was easy to steal from an apartment block because "all I really had to deal with was somebody coming down from their apartment to get in their vehicle, and at that time in the middle of night it's not usually that often."

2. Be aware that your car model might be a target
Fuller used to love stealing Honda, Toyota, Acura, and General Motors vehicles because "they have good resale value so the parts are in demand. It's as simple as that."

3. Don't keep spare keys in your car
It sounds so obvious, but people really do it - in fact, Fuller told 20/20 that for 90 per cent of the vehicles he's stolen he used the car's spare keys to do it.

"Glove compartment, center console, door, change tray, you name it, it's there. I found it in all those places," Fuller said.

4. Be aware of secret keys
"A lot of people don't know that they have a valet key inside their vehicle," said Fuller of the keys which can unlock the driver's side door and start the car. Your car manual will advise you of whether you have a valet key or not.

5. Don't leave your window open when you're not inside
This is the biggest mistake you can make.

"A window that has enough room for me to stick my fingers in, I can get out of its track by rocking it back and forth," Fuller explained.

"Then, I can pry the window out of the track enough to where I can get my arm down in there and unlock the vehicle."