My husband has locked his keys in the trunk on a couple of golf outings. He generally keeps his wallet in his pocket. I looked at all types of devices for hiding a key on the exterior/underside of the car and just didn't feel they were secure enough from thieves. I found this little device online and decided to buy it. The only downside is that even though the open key space is pretty wide, the only key I was able to purchase for his car door without the thick plastic top was still wider than the allowed space. My remedy for this was making a crescent shaped cut into the material on one inside edge with an x-acto knife. Voila! The key now lies flat in the holder as intended. The small modification did not seem to interfere with the integrity of the product in any way. My husband seems happy with this extra measure of precaution - especially when his golf outings can sometimes be an hour or more away from home.