Double cylinder deadbolts are keyed on both sides. These should only be used on interior closets or maybe an office to keep kids or intruders out. Many times they are found at garages and exterior doors of the home. Single-cylinder dead bolts should be used at the exteriors so you and your family can escape a fire without needing a key. If an intruder wants in, let’s face it, he can get in. Windows are easy to break. Doors in the home can be kicked in, or locks picked in seconds. Windows and doors should be accessible without keys for safe exit during an emergency.
At one El Paso home this week I even found a single-cylinder lock on each side of a garage door to the kitchen. No door handle on the garage side and no way to open the door if the other side was locked. I will add a photo to my Image gallery soon.