Many people think that double cylinder deadbolts offer twice the security as single cylinder deadbolts.
The fact is that double cylinder deadbolts are only necessary for specialized applications such as doors with glass on or near the deadbolt. Intruders can break the glass, reach in and release the thumb turn on single-cylinder deadbolts. Since double cylinder deadbolts require a key to lock or unlock both the exterior and interior of the lock, ultimate security is enforced.
But be careful. Many communities prohibit the use of double cylinder deadbolts because they may cause serious problems in an emergency where a quick exit is essential. If you do use double cylinder deadbolts, make sure to keep a key nearby and ensure that everyone in your home knows its exact location.