A garage door opener remote could be a key to your home. If left out visible in a vehicle, it could attract robbers, especially since your home address is on your car registration which is typically in your glovebox.
Try to purchase a garage system with a garage door opener that has a keyring so you could easily attach the opener to your keys. Or, bring the remote control with you in your purse/backpack when parked in public places, or in front of your home. Or, simply make sure your garage opener is not visible from peeking inside.
Garage Door Opener Remote theft has been on the rise, according to my local news.